As mentioned elsewhere this:
> So… My first instinct when I read debunking efforts like this is to try to check out who is doing the debunking.
is the definition of "ad hominem". Attacking not the position a person holds, but the person.
Discussion is what we have here. The comment in question, a part of the discussion, implied that the point what was made by the author is questionable because of who the author is.
This IS NOT the case. This is akin to simple research. Imagine you want to build a computer, and in your research you find The Verge's guide. You look up The Verge and check that it is simply not a good source for such information.
There is no one against another here. It is one with an argument, and one neutral, consuming the content, with no position whatsoever.
> Like it or not … when an institution positions themselves like that, it makes me wonder a little bit about whether they really can support unbiased environmental science
Maybe the university can't, maybe the author pulls it off regardless. Has anyone ever seen someone do good work at a shitty company? It wouldn't quite work to say "can anyone tell me if someone who studies or teaches at a university with a questionable line of PR on website can possibly be unbiased about environmental science?", the answer is something like "of course that's possible, to the extent that any human can be free of bias.. to give a useful answer maybe tell me what person and more importantly what research are you thinking of?", which would bring us to a point at which the comment never arrived.
But if someone just "wonders", then it's supposedly not okay to ask them to make up their mind before they post, or at least say what is keeping them from doing so. It's like "I'm not entirely sure I'm convinced most people would agree that" and other phrases, it does imply something, as faintly as it may be, but with plausible deniability. Generally speaking I find that worse than even a direct false claim, which I can correct, in these instances it's like saying the emperor is naked, and people go "there is no emperor, how rude".
Still, I don't think calling the post a debunking effort is the core of the comment, but the CV analysis. Especially the part where the commenter considers the post credible: "[...] I tend to find her post credible here on general this-looks-like-a-fellow-academic grounds."
The commenter then brings his research to the institution, and make an affirmation on a possible bias. Possible being the key word, what makes the whole period kind of useless. Yes, we can't correct it since it is not false (nor true), but we also don't have to correct it, as it holds no weight.
In the end, I'd sum the comment up as, "I consider the post credible as an academic, but won't be surprised if proven wrong.", and I would definitely not call this ad hominem. Especially given the commenter has not positioned themselves for or against the content, but as a passive reader.