Joe had wanted to say something cool, but he slipped and fell off the barren giant's body before he had the chance.
That was when he realized that the gunk covering his body wasn't blood or anything, it was a slick and sticky petrol-like substance.
The barren giant only had a sliver of health left, so the players were less fighting it and were rather fighting each other for who could get the last hit.
The barren giant, on the other hand, had lost its will to fight, running back towards the cliff hoping the Mountain Bandits could come and hold the players off.
But a few eagle-eyed players (mainly the Rangers) noticed that the mountain bandits' hideout at the side of the cliff was completely empty. Some time during their fight with the barren giant, the bandits climbed to the top of the cliff through a secret passage to escape.
Looks like they had never intended to help the barren giant from the beginning.