This is not quite how it works. I was a hiring manager at Facebook for several years. It is made very clear to EMs that team selection is not a second interview or extension of the hiring process. We do not consider team selection part of hiring.
Now, obviously there is a degree of self selection. And if you have multiple engineers coming from boot camp you can, of course, choose an engineer you feel would be more successful. That’s OK.
But I couldn’t turn an engineer down because I felt they wouldn’t be a good ‘fit’ on my team: they’d already been through the hiring process. Conversely, it absolutely can and does happen that people go through the specialist interview loops and end up in a completely different role. For example, you could have spent your entire career writing iOS client code and join a backend server team, no problem.
That’s the theory, in practice of course for some people it does turn into a second phase of hiring, which is very much not the intention.