I agree with Parnel, perhaps in a different text, that is only an assumption that you were bumped by deadhead staff. They are all prebooked and seat assigned.
You were only "standby" for that flight and perhaps passengers with confirmed tickets showed up at the end.
If a uniformed pilot did board an aircraft as was noted by another poster, he/she was deadheading to ensure that another flight down the line was fully crewed and not delayed. They must fly!
Your situation was unfortunate, but if a concierge was kind enough to come on board and look after you, I'm sure it was warranted and necessary for one of many reasons. But you were 'standby."
SC