Happens on lots of aircraft. Condensation is the most obvious cause. On some aircraft configs on really wet and windy days rain can blow in and remain in some cabin crevices after the door has shut.
IMO it takes a lot of water to deem moving passengers as necassary but if there were spare seats then they are free to move. Passengers don't normally ask to move after take off any other time. As for hibernating..... that will be in the galley or crew rest. With the lights down and passengers sleeping, the last thing people want is the crew doing a jig in the cabin. It sounds like you don't particularly like crew if i'm being honest.