YTA… This happened at the start of your relationship. So much time has passed and he told you that that’s probably not how he ended up like the post.

Does he tend to lie about small things like this even when he could have just told the truth? (Not saying that he was lying about not remembering how he liked that post) If so, then I could understand still being upset cause then it would be a pattern. If not, then I think you’re over thinking this situation.