Some of it remains a mystery
Nobody really knows how each College and Faculty organises their interviewees. Some applicants Interview at one college, some at four or five. If you get “pooled” or sent to other colleges, it’s still quite possible you will receive an offer from your original choice. Similarly, if you don’t get pooled it doesn’t necessarily mean you weren’t good enough – perhaps the tutors were so impressed that they didn’t feel the need to send you elsewhere.