The GP would have had to appeal only to the expert’s opinion, with no actual evidence, but the GP actually gave a lot of evidence to the expertise of the researcher in the form of peer reviewed papers and other links. That’s not an appeal to authority at all.

Please check the textbook - that fallacy asks to accept a claim based on authority. In this case, we have a negative-spin troll (negativeonehalf) spreading FUD about an established subject expert ("a lot of other stuff wrong") with one falsehood after another (paper not peer reviewed, Kahng funded by Cadence, etc). No authority is needed to debunk the troll's claims - they are not supported by anything, basically made-up nonsense.