This is not an ad hominem argument. This is merely blowing things out of proportion. This would be ad hominem (and non-sequitur):

"You're watching dancing bunnies, and you dare suggest we should remove the parens after sizeof?"

Attack on the person (watching dancing bunnies), used to discredit an unrelated opinion (parens after sizeof).

To be fair, he's referring to the code `sizeof(*p)->reference`, in which case I'd probably shoot the writer too.

I'm sure he'd appreciate a memo from Sam Altman about gratuitous negativity.