It may be poor sportsmanship, it may be bad form, but to qualify as an ad hominem, there must be an actual attempt to denegrate the arguer. What you have here is bad manners, which you are entitled to point out, but not an ad hominem, except by stretching the definition beyond anything easily warranted. Is a contempuous smirk an ad hominem argument? Jerky behavior comes in categories--you can't just call everything dismissive an ad hominem argument. The boat will sink under the load, and the phrase will become valueless. A fallacious argument requires, first of all, an argument.
Well, this has already gone on too long, so here's one more attempt to close the gap. I think I agree with you with a caveat.
The dictionary definition says, " ... marked by an attack on an opponent's character rather than by an answer to the contentions made..." So I suppose that in the context of your friend's 'response', whether it was an 'ad hominem' attack depends on whether, by assigning my response to an unrelated group ("creationists") to which he referred in derision, he was attempting to launch "an attack on an opponent's character." My point would be that there would be no other reason to purport to align me with an unrelated group.
He surely didn't do it to build me up. Be that as it may, I guess I'll be satisfied with the admission of your friend's "poor sportsmanship [and] bad form."