It's not that it's not ad hominem if it's true - ad hominem has nothing to do with the veracity of the claim. It's not ad hominem because it is purely based on the discussion at hand. An ad hominem attack is attacking a person's character or other traits instead of their argument. Everything I said in that thread was purely based upon what was posted, and thus by definition could not be ad hominem.
People have a nasty habit of confusing "insulting" and "ad hominem." Yes, what I said was, in some capacity, insulting. It needed to be - you cannot accurately address views of that sort without being insulting, because they are, in a word, stupid. The idea many people have that "there's no such thing as a stupid belief" is horribly counterproductive if you want a community capable of reasoned discussion.