There's quite a few same-sex educational organizations around. I think you're confusing this with equal opportunity employment, which only applies to certain sized companies or ones that take Federal money.
Perhaps a better comparison would be to women only gyms. If you google "are women only gyms legal" you'll come up with a slew of articles suggesting women only gyms are probably not legal, up until the various state legislatures pass specific laws making them legal.
I am not a lawyer, I have no good idea if hackbright is operating legally or not, but I wouldn't be surprised to find what they are doing is not legal.
