I don't write what the code does or even what "I understand the code to do". I explain choices, especially ones that the next developer or my future self is likely to misunderstand when looking at the code.

I've always said coding is a cottage industry!

It's luckily rare for people to add wrong comments, though (and those who do should be publicly fustigated).

By the way, please never state something as it were the truth if you're not sure that it is. Saying "I think" is perfectly fine, and might save people days of investigation.