Unlike Aaronson, he actually is on the forefront of Busy Beaver research, and is one of the people behind the https://bbchallenge.org website
Extremely bad ad hominem, I enjoyed Aaronson's read, nothing wrong with it.
Colloquially, I understand it's easy to think it means "saying something about someone that could be interpreted negatively" because that's the context it is read in it when it is used.
The meaning is saying a logical argument is incorrect because of who wrote the argument.
It is implying that claims from the article like "Then, three days ago, Tristan wrote again to say that mxdys has improved the bound again, to BB(6)>9_2_2_2" are not real results. The justification for these not being real results is solely based off whether author is actually on the forefront of research.
OP isn't making a ad hominem fallacy in a logical argument sense - it's not saying "Aaronson is wrong because he's not a frontline researcher."
But you're absolutely right to feel uncomfortable with their approach. There's something off-putting about dismissing someone's reporting of research developments, even if you prefer more comprehensive coverage, or there's more interesting things to say.
The thing is, if that's ad hominem, so is any recommendation preferring one second-hand reporting over another -- ex. "if you want the actual news, read Tucker, not Krugman" isn't an ad hominem towards Krugman.
Another example we see often on HN: saying "you should read the actual paper instead of this pop science" is a quite frequent, quite agreeable, and yet dull, contribution on say, a Quanta article. Yet, I imagine we agree this isn't an ad hominem.
The real issue might be that OP conflates two different things: being a primary researcher versus being a good science communicator who accurately reports on others' work.
Both roles have value, and questioning whether someone has filled one role doesn't necessarily invalidate their ability to fill the other.
(this helped me understand my odd frustration with the dull comments on science articles: I emotionally engage with it as being mean / out of bounds, but its true, and in reality, what I'm frustrated with is there could always be a more detailed article, or even paper, but yet we all must publish)
But how you justify that could be one. If you are just attacking the person instead of their reporting I would call that ad hominem.