That's not an appeal to authority. The essays themselves are substantive; he didn't say, "Chollet says so, thus it is so." More importantly there is an element

That's not an appeal to authority. The essays themselves are substantive; he didn't say, "Chollet says so, thus it is so." More importantly there is an element of misuse going on here: the "fallacy fallacy" if you will. Fallacies like ad hominem and appeal to authority are very often mis-cited without substantive refutations. But in the absence of other qualifying data it is absolutely relevant to a dialectic session that you mention authorities in a subject matter. When we talk about things like consensus in sciences (like climate change, for example), that is a valid appeal to authority. You don't have enough time or expertise to verify specialized information or even qualify its context. At some point you absolutely need to appeal to authority just to be productive. If you can assess data yourself then that's obviously better, but in the absence of that capacity the assertion of various authorities is a valid first heuristic.