What was unseen when Qur'an 6:50 ("I do not tell you... that I know the unseen") was revealed?

Question

Say, [O Muhammad], "I do not tell you that I have the depositories [containing the provision] of Allah or that I know the unseen, nor do I tell you that I am an angel. I only follow what is revealed to me." Say, "Is the blind equivalent to the seeing? Then will you not give thought?"
_{Qur'an 6:50}

The Prophet Muhammad is aware of many things which are unavailable to the rest of humanity. For example, I looked at Paradise and saw that the majority of its residents were the poor; and I looked at the (Hell) Fire and saw that the majority of its residents were women (Sahih al-Bukhari 5198). As far as I know, not even any other prophet had this knowledge.

I found this tafsir:

This verse was revealed about Abu Jahl and his companions al-Nadr Ibn al-Harith and 'Uyaynah, and then it was revealed about the clients.
_{Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs}

This indicates there's something specific which was unseen to the Prophet at the time the verse was revealed.

Question: What was unseen when Qur'an 6:50 was revealed?

Answer 1

As the tafsir you quoted says, it seems that this ayah is a response to the People of Makkah and their demands from the prophet. (For instance, they wanted him to turn a mountain into gold.) Allah is telling the prophet to inform them that just because he is a prophet doesn't mean he can do or know supernatural or unseen things.

This is from the online english version of Tafhim ul Quran by Sayyid Abdul Alaa Maududi:

The foolish people have always had the silly notion that a Prophet of Allah must be supernatural and capable of performing wonderful miracles. For instance, they expected that a whole mountain should turn into a mass of gold at his bidding: that the earth should throw out treasures by his orders: that he should be able to tell the people all about their past and future: that he should be able to locate a lost thing and foretell whether a sick person will get well or die and whether a pregnant woman will give birth to a male or a female.

According to Maududi, this unseen is referring to the demands that the people were making from the Prophet (SAW) which were ridiculous because they were asking for things no human at the time could know, so Allah is making the Prophet (SAW) emphasize the fact that he is human.

In conclusion, it seems that there was no specific 'unseen' being spoken about but, rather, this is referring to the general things that the people were asking of him that he didn't or couldn't know.

Additionally, I think you are misunderstanding the tafsir you quoted. It is not saying anything about the 'unseen' in the ayah. It is just talking about the purpose of the ayah. It was revealed about Abu Jahl and his companions. But, later it also applied to the clients. So, this is in fact not 'indicating there is something specific which was unseen' as you stated.