Why? He can't criticise his critics, unless they're scientists of his own standing? I don't know who wrote those rules but I don't remember reading them.
Are you sure this is not just you painting meaning and intensions on the exchange because of the people involved and preconceived ideas about "exalted professors" snottily dismissing mere grad students etc?
I think I read the biggest part of the appendix in the linked article and it doesn't come across as what you say. It comes across as irrelevant and unnecessary. The passage was put in an appendix but it really belonged in a blog post, or a tweet, but certainly not in a scholarly article. But other than that, it wasn't even particularly vituperative, just indulgent, really.
It certainly wasn't "insult[ing]" as the parent claimed.
And then of course he removed it from the appendix with a note taking responsibility for it. Yet here we are, still talking about it, as if he stabbed someone in the face or ate babies alive, or anyway whatever a scientist's reputation can reasonably be expected to never recover from.