Earlier quoted context omitted.
You might prefer a looser definition of ad-hominem, but I think that the technical definition holds value. This looser definition reads like a means of implying that the poster's intent was different that what it was.
It is mildly humorous that we've gotten this far in and you're telling me "hm I don't like the definition in the dictionary, we should pick something more technical" (???) I have a CS and law degree and IMHO the divide here is the CS people tend to believe "ad hominem" has a technical definition beyond, well, the definition
To argue that someone's argument is wrong because of who they are is a logical fallacy, and something people actually do quite a lot. The term for that and as far as I know the only term for that, is 'ad-hominem.' To attack someone's character instead of something they wrote is usually not considered very nice, but is not a logical fallacy (unless we're talking about the abusive form of ad-hominem, but I don't think that's what we're talking about here.) Given that the former needs to called out on occasion, that that one can use other language to call out the later (just say 'personal attacks'), it makes sense that reserving the term 'ad-hominem' for the former use makes practical sense.
Even if you don't agree with my reasoning that it's better to reserve the term to refer to the logical fallacy, many people really do use the term exclusively to refer to the logical fallacy and don't use the dictionary definition you listed. Citing a dictionary to resolve a language usage dispute is a bit of a dodge because dictionaries are typically descriptivist when these disputes are inherently prescriptivist (or at the very least stipulative.)If people are getting confused by what you are saying, it's better to clarify than to die on the hill of what the correct definition of a word should be.
All of that is beside that fact that the reason people get upset about this issue--about the definition of ad-hominem--is that people using the later definition are often performing a bit of equivocation. They are using the later definition, which does not refer to a logical fallacy, to imply that a logical fallacy has occurred. This is a sort of slippery and dishonest debating tactic and I think that it rightly upsets people. If you did not intend to be deceptive, that's all well and good, but understand that that's a big part of why people are getting upset with you.
edit: Removed the first sentence in which I accused that guy of arguing in bad faith. There's nothing else in this comment that is objectionable, AFAICT.