Fire does hurt predators. I doubt the torch Weyland used in the movie was very hot. Comparing Pyro to a home made flamer.. Yeaah very smart. + Weyland only hit the Predator's armor, which doesn't burn. If he had continued for some time to burn the Predator, he would have gotten quite "sweaty" under all that armor.
+ Predators have been burned in the comics before.
This is a Spite thread, Predator doesn't really have a chance..