This is neither the first, nor last instructor, to not have a clue about the workings of an engine
That strikes me as more than a little worrying. When I learned to fly a microlight in 1990 the syllabus included basic engine (both 2 & 4 stroke) theory. I was, perhaps, fortunate that I already had years of practical experience with motorbikes and cars. But nonetheless I still ended up having a disagreement with my instructor (Hi, Mike) over fuel/oil ratios - it was 2 stroke pre-mix with the Rotax. The question was what is preferable: too little oil or too much? I said too much, as I had practical experience of what the other lead to. However he pointed out what I hadn't appreciated - more oil in the same volume of fuel mixture means less petrol, and consequently a lean running engine. I was initially not convinced, but then realised that it's very rare to have a car or bike operating at full power for more than a few seconds, unlike an aircraft taking off and climbing to cruising altitude, so the situation is rather different.
Back then full engine management systems were not universal, and most drivers had a reasonable idea what went on under the bonnet. Nowadays there is virtually nothing you can do with a new car, so even those who do have an understanding are helpless. But since the majority of light aircraft still rely on stone age technology, a good understanding of ignition and fuel delivery SHOULD to be taught to all students.
As to listening and learning from "old hands" - I've flown quite a bit with a local pilot in his C150 and remember one evening when he did the run up checks and found a significant rev drop on one mag. He spent some time trying to clear it with mixture leaning, to no avail, and we taxied back to the hangar and discovered a plug with a nice globule of lead across the electrodes. I am also aware of the "cut the fuel/mixture and continue cranking" advice if a fire breaks out whilst starting, and the "open throttle and close mixture" method of dealing with over priming is also familiar to anyone of my age. This sort of knowledge should be imparted more widely than seems to be the case in the OP's incident, even if it means upsetting a younger FI.