CaptainMidnight. Legalities of keeping pax on board is a simple one. If the engineering crew thought it was possible to repair the aircraft in time, then to save time and the hassel of deboarding the pax and thier luggage, they keep the pax on board.
Lets say if a strobe light or a landing light blows then its a simple 10 minute fix. Fuel issues are not so simple but still a quickish fix. If it was deemed that the fix would take longer then the pax would have debarked. No passenger would be denied to leave the aircraft. And come on! Its an A380. Not a 717/MD80. They aren't small. Passengers can walk about and what not.
They would have turned on a movie, and served copious amounts of booze. And when that happens the captain wouldn't remove the pax because the Ops Manual would not allow them to fly. So in effect, the captain was doing the passengers a favour.