Not baseless. Perhaps not correct, but not baseless. And exactly how is IDing you as possibly being PD'oh an "ad hominem"? If you don't know who he is, how did you know you were being insulted?
Also note, even if IDing you as Pd'oh could be considered an insult, it's still not an ad hominem, unless I use that ID to dismiss your arguments, which I haven't done.
Rememeber: "You're an idiot, so your arguments have no value" is an ad hominem. "You're an idiot" is just an insult. Important difference.