Yes, the interview is a good sign. I think almost everyone in the US who applies is offered one, so it’s not significant domestically. International students are encouraged but not required to interview (because interviewers aren’t always available). Sounds like they are making sure you have that opportunity, so you should certainly take advantage of it.
It’ll be a friendly conversation (NOT a kind of oral examination), designed to give the interviewer a sense of your personality and your understanding of what you’re getting into. It’s also explicitly designed to give you a chance to ask questions about the school. Be prepared to talk about favorite books, hobbies, etc. (again, not a test but ice breakers – i.e. prompts to get you talking comfortably) and to ask a few questions of the sort not easily answered by reading the school’s website. Your interviewer may not be able to answer your questions on the spot (especially if they relate to a specific major), but will get back to you or put you in touch with someone who can answer.
Good luck! Judging from what you’ve written here, just be yourself and you’ll make a good impression.