i know refuelling was taking place because there was a fuel bowser attached to the aircraft. by the time i got to board the bowser was detached.
Perhaps not - could have been a small uplift, how long had the AC been on stand etc.
Yes, you are allowed to re/defuel with PAX on board (subject to SOPs allowing it). You may do this with them boarding (the seatbelt signs will be OFF when you get on). You may also do this while they are de-planing. In my opinion this is wrong (from a safety point of view at least). If a person is getting off the aircraft, they will be in "collect hand baggage" mode. Try to then tell them that they need to get off PDQ and they will likely carry on looking for their baggage.
RIX