I wouldn't call this an ad hominem attack. You've got to be able to say that someone is wrong (even that someone is often wrong) without being considered to be attacking them personally.
Why logical fallacy? I didn't say "ergo Yegge is stupid" or "don't trust a word the man says". I just meant that it's worth keeping this in mind when he engages in future-telling again. FWIW I do enjoy reading his essays, even when I think they're wrong.