The error (in your telling) is equating knowledge with confidence. Knowledge is knowing you might be wrong about it all. The advice to spend one’s life questioning isn’t a smarmy nothing; it’s the only truly sensible approach when you step back and think about it.
Then, when we have two e.g. physicists, who both know quite well what they are discussing, and one of them is more famous and potentially through their prestige succeed in ridiculing their less recognized colleague, we are at the "appeal to auhority" position.
One famous example is that of Ernst Mach who was was positivist (i.e. did not respect theory whose constituents you could not directly measure) and ridiculed Boltzmanns kinetic theory of gases because Mach did not believe in atom theory (!). Boltzmann's theory was effectively attacked precisely from position of authority.
So, if a layman and a physicist argue what is possible, it is very likely while both of them may be wrong, the layman likely does not have any understanding what their position implies.
So in my opinion, you can have a pathological appeal to authority sort of situation only when two equally skilled persons have an argument an the institutional prestige of one of them is used as an appeal for them.
At the risk of argumentum ad logicam, this is a textbook example of survivorship bias. History is also full of people who were adamant they were correct in the face of ridicule, and turned out to be wrong anyway.
Your broader point is right; obviously if we stop to poke at certain assumptions, the occasional one will collapse.
However, the pathway you’ve just suggested is less practical than you think. The GP is talking about a systematic, coordinated exploration effort of known unknowns.
Metaphorically - he/she is saying that there’s more likely to be gold at the unexplored end of gold mine, not in the excavated dirt.
It’s a fair assumption to keep in practise.
that's not a great definition... I know I might be wrong about flying UFOs, but that doesn't count as 'knowledge', does it?