Man, I really don't want to be negative but think you just got scammed. My guess is that once you get there, you will find that anybody off the street can join the Amateur MMA Program if they sign up for $125 a month for lessons.
I'm also guessing that they sent out a whole lot of these invites, to more fighters than they really have room to accommodate, knowing that most prospective fighters won't go ahead with moving out there.
They might have done some cursory examination of your record, past opponents, etc. to see if you are worth putting some time into to see if they can make more money off you later if you go pro. But I think this is pretty much a one sided deal. They're not taking much of a leap of faith with you. They have nothing to lose, you're paying to be there. On the upside, yes, I'm sure the training will be fantastic.