Some people say that I should not read The Holy Quran tafseer alone in my house. I have to take guidance from some A'lim who knows vast knowledge about Quran. If I read it I may be misguided and may not get the right meaning.
As a non-alim, you can benefit from reading the commentary and translation of the Quran on your own. The only thing the Ulemas have advised against is drawing your own conclusions and coming up with fatawas. Those are things that require consultation with someone of knowledge and in some cases the consensus of many Alims.
I think your friend has confused this bit of the advise with simple reading.
I'd like to add that tafsir books may differ according to the time they were written and the emphasize of the author. For example many older tafsir books included so called israeliyat which are stories, tales and legends scholars have got by consulting people of other Abrahamic religions like Jews and Christians. But one couldn't relay on blindly on such stories. This is one of the reasons why one is always encouraged to ask people of knowledge (16:43).
In Islam oral transmission that means learning by listening or asking a teacher is highly appreciated see for example: this hadith from sunan abi Dawod is about the importance of sanad or this one about spread what our Messenger (peace be upon him) said to those who were not present. Also a version of this hadith about the importance of learning about our religion in the book of Imam at-Tabarni in his kabir is narrated with the following addition (note this is my translation and it's not literally - take it with care, this is the case for most other translated texts in my answer unless I quoted a source):
He to whom Allah intends to do good, He gives him insight into religion... Certainly sciences is taken by oral transmission and by learning from "teachers".
من يرد الله به خيرًا يفقّهه في الدين...إنما العلم بالتعلُّم، والفقه بالتفقّه
Scholars like ibn Sireen or Imam Malik have been saying:
"The knowledge of hadith (in the same manner all other religious subjects) are included in the deen. Therefore before acquiring knowledge, be aware from whom knowledge is acquired".
Sheikh al Quradawi said:
لا تأخذ العلم من صُحُفي ولا القرآن من مصحفي
Don't take science from somebody who reads from papers nor the Quran from somebody who reads from a Mushaf (copy of the Quran) -or have memorized the Quran only from the Mushaf-.
The issue is not when you read and understand nor when you read and doubt about your understanding in both cases you will do an effort to check your wisdom. The issue is when you read in a book and think you've understood, while actually you've misunderstood (therefore saying I don't know is a valid fatwa if one has no clue: Is there a source for "Whoever says I don't know has given a fatwa"?) in this case you may stick on what you think is true and spread a mistake to anybody who asks you.
And this is or was the view of the majority of scholars (Quote al-Khatib al-Baghdadi):
لا يؤخذ العلم إلاّ من أفواه العلماء
The science of religion can only be acquired by oral-transmission.
يؤخذ العلم من أفواه العلماء ولا يأخذ من بطون الكتب
The science (of religion) has to be acquired by oral-transmission from people of knowledge and shouldn't be taken from the pages of a book.
So without guidance one should avoid interpreting any kind of religious text as this is a big sin and serious matter.
Therefore students used after reading or memorizing books to search for a scholar to test and approve them which means they would get a permission to teach that topic or special book or matter and become a kind of authority in it.
And Allah knows best!