The teacher very likely didn’t understand either.

Physics isn’t considered an important enough subject to hire qualified teachers for. My state substantially simplified our physics qualifying test recently because it was “too hard” - and already it solely covered CM.

This will also factor into how they treat you as a teacher - you aren’t essential, you’re kind of weird and sometimes you annoy the math teachers by begging them to shut up about “cross multiplying.” I guess some states see physics as a “core” science - but where I am I can think of two high schools in a two hour radius that even offer intro physics.

In general, most of the people who sat in QM with me were able to find substantially better paying careers than I did. If you pursue mathematics beyond calculus, then usually you are qualified for jobs that will either pay you a fair wage or at least treat you better than teaching does.