Don't be mistaken, they liked something about you because they are very selective, so pat yourself on the back!
I have no idea on their handling of international students (I'm one myself) in regards to applications. On one hand, they might be interested in bringing people from elsewhere for diversity reasons, but admissions are supposed to be (at least in theory) need-blind. And they do offer financial help to international applicants if they want them enough. Whether they advertise it or not, all schools have a discretionary budget for scholarships that can go to anyone. It's only Federal aid that is limited to US citizens. So if they think they have the next Oscar winner among the applicants, they can lure that kid, no matter how poor, with scholarships so that they can compete with other schools who are likely to want him/her too
Also, don't use interviews as you guide because some schools simply don't interview anyone for some programs. They do their selection based entirely on the portfolio submitted, and that doesn't mean it's easy to be admitted (if anything, I feel they make it harder for you to prove you'd be a good fit).
You mentioned you're not sure what you applied for? If it was for writing, many programs don't interview writers at all, so there's that
Congrats on your admission! Feel good about it because it's definitely not that easy!