If there was no known fuel leak there is no need to shutdown. In this case crew seem to be unaware of fuel leak, later
PR teams tried to spin it as ~10 gallons of hidden oil.
Look at the fire photo posted, evenly intense to the tip.take a close look at the flame pattern.
My theory and speculation is the fuel leaked during fuel jettison from the wing tip jettison.
Perhaps the wing filled the empty cavities with fuel during the fuel jettison approx 35 tons guessing. That is 17.5 tons each wing jettison point dumped in 20 minutes.
The ignition was on selecting idle reverse thrust.
Fire services at Singapore are definitely world class as is the airport.
If the fire services reported fire is "under control " within the first minutes.
It is hard to believe but possible especially if that fire went out after a short time, expending all the pooled fuel.
"No fire" means no evacuation after the first 2 minutes.
Just a theory but worth considering for those who speculate prior to investigation release.