I'm not sure which "confusion" you believe to be addressing, as I agree with very much of what you are saying, in the first place. When I say "day trader", I include "week trader" and "month trader", anyone who is trying to take advantage of fluctuations around a some (perhaps rising) price level, as opposed to a long term investor who is waiting for either a longer time, or a larger price move to some higher level. The long term investor usually does not expect to buy again, after selling.
With TSLA, the opinions about whether a short squeeze (of some magnitude which would be worth the name) can occur, seem to be split. And if that is on the edge, then a number of day traders can make the difference.
I'm not a stock market expert in even a "hobby" way, but if I am looking for a criteria where our views differ, it is probably that I don't see "trading volume" as a constant number. The short squeeze is likely to happen if there will be a development that causes the number of sellers to drastically reduce, while on the buyer side, the shorts will not only want to cover because of that development, but additionally the price increase will be large enough to *force* them to cover, since they cannot afford to take a larger risk.
In the case of VW (which apparently is an extreme example), the situation occurred because Porsche, by itself, was enough in control of the seller side to keep the shorts from "escaping" through some "leak".