is this common?

I started out on a unit and wasn't happy there. As a new nurse, it wasn't so much that I couldn't handle the stress of working on this unit, I just didn't really want to do it. I think the worst part was knowing that I wasn't giving my patients 100%. Don't get me wrong, I did everything I could for them, but I felt like there was a piece of me that was missing.
So I gave HR a list of units I'm interested in, and they called me and said they had an opening on my dream unit. However, there isn't a posting for an opening on this unit on their website and I also checked as an internal employee, and there's nothing there. Would you assume that I'm the only one interviewing for this position? Is it common for a unit to have openings and not advertise them? If so, why would they do that? I know my manager talked to the manager on my dream unit, so I'm hoping she put in a good word for me.
I just feel sooo lucky to have this interview, ever since I found out about it I've been smiling! The thing is I know how difficult it is as a new RN to get a job on this unit. So I'm keeping my fingers crossed until then.
Thanks!