Yeah they are bearing the burden of these people due to the fact that they followed their "self-made shari'a" instead of Allahs shari'a which was described one verse earlier (6:145)!
Say, "I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine - for indeed, it is impure - or it be [that slaughtered in] disobedience, dedicated to other than Allah . But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], then indeed, your Lord is Forgiving and Merciful."
pretending that Isra'el (Ya'qub) had prohibited for himself as quoted in (3:93).
See also in surat aal-'Imran (3:93-94):
All food was lawful to the Children of Israel except what Israel had made unlawful to himself before the Torah was revealed. Say, [O Muhammad], "So bring the Torah and recite it, if you should be truthful."(93)
And whoever invents about Allah untruth after that - then those are [truly] the wrongdoers.
In this context ibn Kathir quotes a hadith from Musnad Ahmad:
Imam Ahmad recorded that Ibn 'Abbas said, "A group of Jews came to Allah's Prophet and said, "Talk to us about some things we will ask you and which only a Prophet would know." He said, "Ask me about whatever you wish. However, give your pledge to Allah, similar to the pledge that Ya'qub took from his children, that if I tell you something and you recognize its truth, you will follow me in Islam."
They said, "Agreed." The Prophet said, "Ask me about whatever you wish." They said, "Tell us about four matters:
What kinds of food did Isra'il prohibit for himself
What about the sexual discharge of the woman and the man, and what role does each play in producing male or female offspring
Tell us about the condition of the unlettered Prophet during sleep,
- And who is his Wali (supporter) among the angels"
The Prophet took their covenant that they will follow him if he answers these questions, and they agreed. He said, "I ask you by He Who sent down the Tawrah to Musa, do you not know that Isra'il once became very ill When his illness was prolonged, he vowed to Allah that if He cures His illness, he would prohibit the best types of drink and food for himself. Was not the best food to him camel meat and the best drink camel milk" They said, "Yes, by Allah." The Messenger said, "O Allah, be Witness against them."
The Prophet then said, "I ask you by Allah, other than Whom there is no deity (worthy of worship), Who sent down the Tawrah to Musa, do you not know that man's discharge is thick and white and woman's is yellow and thin If any of these fluids becomes dominant, the offspring will take its sex and resemblance by Allah's leave. Hence, if the man's is more than the woman's, the child will be male, by Allah's leave. If the woman's discharge is more than the man's, then the child will be female, by Allah's leave." They said, "Yes."
He said, "O Allah, be Witness against them." He then said, "I ask you by He Who sent down the Tawrah to Musa, do you not know that the eyes of this unlettered Prophet sleep, but his heart does not sleep" They said, "Yes, by Allah!"
He said, "O Allah, be Witness." They said, "Tell us now about your Wali among the angels, for this is when we either follow or shun you.' He said, `My Wali (who brings down the revelation from Allah) is Jibril, and Allah never sent a Prophet, but Jibril is his Wali." They said, "We then shun you. Had you a Wali other than Jibril, we would have followed you."
On that, Allah, the Exalted revealed,
قُلْ مَن كَانَ عَدُوًّا لِّجِبْرِيلَ
(Say: "Whoever is an enemy to Jibril...'') (2:97).'' (qtafsir)
See also in (4:160-162):
For wrongdoing on the part of the Jews, We made unlawful for them [certain] good foods which had been lawful to them, and for their averting from the way of Allah many [people],(160)
And [for] their taking of usury while they had been forbidden from it, and their consuming of the people's wealth unjustly. And we have prepared for the disbelievers among them a painful punishment.(161)
But those firm in knowledge among them and the believers believe in what has been revealed to you, [O Muhammad], and what was revealed before you. And the establishers of prayer [especially] and the givers of zakah and the believers in Allah and the Last Day - those We will give a great reward.
I recommend you to read the relevant tafsir in qtafsir. And also read for example the story of the cow (2:67-71) and other stories in surat al-Baqara etc. for examples for the transgression of the Jews, also read in al-Baqara
Do you covet [the hope, O believers], that they would believe for you while a party of them used to hear the words of Allah and then distort the Torah after they had understood it while they were knowing?(2:75)
So woe to those who write the "scripture" with their own hands, then say, "This is from Allah ," in order to exchange it for a small price. Woe to them for what their hands have written and woe to them for what they earn. (2:79)
which shows why this happened, and that not all of them were following this wrong shari'a and therefore not all of them were bearing this burden.
So basically they harmed themselves. And instead of questioning this wrong shari'a kept on following it.
Note that the statement:
And no bearer of burdens will bear the burden of another.
from verse (35:18) refers to the day of resurrection as stated by ibn Kathir:
(And no bearer of burdens shall bear another's burden;) means, on the Day of Resurrection. (qtafsir)
So the fact that the Jewish shari'a seems full of hardship is not related to this ruling and it is simply due to their transgression and their manipulation of the scripture and shari'a of Allah.