I cannot agree with what the "instr" did but....
Do not go on an island vacation to dive untill you have mastered the required skills in the pool first..If you have to have any qualms about clearing a completely flooded mask/or no mask then you are not ready for the dives..It should be "no big deal" in your head to do any required skill before you go,should be able to accomplish skill easily with no discomfort...I have seen too many people who can barely clear a mask and get certified and still be afraid of having water on their face..These people are an accident waiting to happen.
I have to say, reading between the lines a bit, that the instructor doesn't seem to have made any big mistakes.
Initially, if you've completed the pool sessions then you should be comfortable with flooding and clearing your mask - this may not be the case but I can understand why an instructor would expect it. It sounds like the instructor's main fault is lacking the "people skills" to pick up on your difficulty with this exercise.
As regards preventing your ascent, the instructor was spot on - he had no way of knowing whether you were breathing or holding your breath. Sorry, but when working with students we have to keep you safe whether you like it or not
At the surface, it's difficult to judge without knowing exactly what happened but in that situation I would certainly make sure I had got the students BCD inflated before breaking contact with them - could this be what the instructor was doing?
As I say, I think the only thing this instructor needs to learn is some people skills but overall I can't see any major problems with what they did.