There's always a chance of getting in until you get an official rejection, and there might be other factors beyond anyone's control over whether or not someone gets in even if there is an advisor to sponsor you. I would say it's definitely a good sign that you had a professor say they would support you! Whether or not you get in, it means that there's someone who believes in your research ideas, and that they believe you have a successful career ahead of you. If you don't get in then you can always apply again next year!
PhD admissions are super random. There are always more qualified applicants than spots for PhD students. It doesn't mean that those who get into schools shouldn't be extremely proud of their accomplishments (because there's so much to celebrate and be proud of!), but it does mean that if we don't get in it could have nothing to do with how well we'd do in a program, or how strong of an applicant we were. Maybe the person reading our applications was just having a bad day at the time they got to ours... You really never know.
I'm curious if anyone else here is waiting on UNC or knows about the process. Or if anyone has been interviewed/talked to a professor ahead of time and still hasn't heard back, or is just waiting after hearing nothing since submitting the application.