The lack of ethnic minorities is an indicator of cultural and behavioral homogeneity, not the definition of it (i.e. the important question is why weren't there any ethnic minorities there?).
And yeah, the teacher's response was unjustified (precisely because hairstyle is such a trivial thing).
and a terrible teaching practice. How could a teacher expect the student's mind to be ready for learning after being made to feel like a freak of nature? "WTF is wrong with you?! Okay, now turn to the chapter on quadratic equations." Did they think a student could just switch gears and turn off the emotional impact? (I'd be a little afraid of the student who could shrug it off.)
Teachers are supposed to inspire learning not setup barriers to it.
(Most of) my teachers weren't really trying to teach us. They were just there to get a paycheck.
To whit: almost half of my graduating class was reported as valedictorian to the colleges they applied to. Why? Everyone with over a 4.0 was valedictorian. How'd we get over a 4.0? Becuase they added the bonus for honors courses on after doing the division, not before. Get an A and a B in two honors courses? That's ((4 + 3) / 2) + (.25 * 2) = 4.0!
This is why I have such a low opinion of education in general.
And yeah, the teacher's response was unjustified (precisely because hairstyle is such a trivial thing).