[fouc]

You called the argument delusional, and therefore it wasn't an ad hominem, so you're right about that.

But, "Delusional" is often associated with name-calling, so it sounds more like you're calling the person delusional, rather than what they said. Something like "This sounds delusional to me" would avoid that confusion.

[yourenotsmart]

I did call the argument delusional, yes.

But even if I decided to call the commenter names, that wouldn't be ad hominem (link above on details).

It's rude, it's uncivilized maybe, we can have qualifications like that. But it's not "ad hominem", because "ad hominem" isn't about "you insulted someone".