I'm gonna attach a part of their email.
well first of all will you have any licenses issued by any country when you come here.. ? if so you do not need to do anything but have that license verified, if not then you will need to do the TSA etc etc and this can be done on a visitor visa
And they go on to say:
if you have not started and would like to do your course within the FAA regs that is perfect, you can do that on your visitors visa, I have been doing it for many years now and it is perfectly legal, the reason that schools want you to get the I-20 is so that they lock you in and when you get here you have no choice but to do everything with them.
We are registered as flight training providers and will take care of all of your needs