Unfortunately sometimes the captain has to make decisions that don't seem logical to the untrained, 100% chance he didn't know how long it would take the engineers, maybe 20 mins ?, on an aircraft capable of flying Vegas-man (i.e.,A330) it would take 25 mins to get the pax off and about 40 mins to get them back on and all seated without the usual 'I,ve lost my boarding card' problems.
No one would have thanked him for off loading only for the a/c to be fixed in 10 mins, also crew duty hours must be close on that sector so he may throw the whole program out by off loading pax and putting himself out of hours to operate the flight - 12 hour delay !!
The trouble is when people get on a/c they suddenly turn into closet aviation experts and question every decision.