According to The Australian newspaper,
"lighters and matches were confiscated in Jakarta before passengers were let back on the flight" Presumably the aircraft was also searched for lighters and matches.
Given the disruption routinely caused by
minor security breaches (Melbourne Airport's spokeswoman's phrase in this particular case today, not mine) at airports with no evidence at all of any malicious intent, it seems quite extraordinary that in the face of clear evidence that an actual arsonist intent on setting fire to the aircraft was amongst the passengers, the flight continued with the culprit(s) aboard.
I don't have the answers; there was little else they could do but continue on, since they were unable to identify the culprit(s), but this seems to fly in the face of the efforts made to rectify airport security breaches on the ground and the level of resultant disruption considered acceptable.
Seriously, it's OK to strand thousands for a few hours because someone turned their back on a door for 30 seconds, but it's not OK to strand several hundred people when you KNOW one of them has already made several attempts to set fire to a long haul aircraft which is about to fly hours from land, because you don't know which one it was? After all, at the end of the day, its clever people with a death wish that bring down planes, not nail clippers or bottled water.