Can a professor I didn't mention in my application accept me as his M.Sc. student?
The simple answer is: yes.

At many schools it is often the case that professors discuss the applicants outside of the official application system. Other professors may have recommended your application to the professor in question, which is why they are asking for an interview with you now. I suggest you concentrate on doing as well as you can for the interview.

Don't worry about the details of their internal process - you don't have any control over that. If the professor wants to work with you, there is usually a way to make it happen.