Asked a professor to be a potential supervisor and she said acceptance isn't her decision

Im so confused. I have been emailing professors at the uni im interested in applying for because I thought I would need an established potential phd supervisor before sending in my application (though it doesnt mention it in admissions).

But the professor i asked replied and said that phd acceptance isn't determined by the professors but by the university, and goodluck with the application. (Though in a nicer tone)

But I didnt ask her for acceptance, just explained my topic and asked if she'd be interested.

Does this mean I dont need a supervisor before applying? The program is coursework heavy, so maybe the supervisor isn't determined until later? Has anyone heard of this?