When one decides to attack a being that's on fire, one sort of anticipates risking getting a little burned - or at least putting a good effort into preventing it. The troll does the latter, raising a shield of shimmery liquid in order to stave off the flames of that initial attack.

"Not looking for an explanation, then?" he says, leaping backwards and out of the way of the boy's trajectory, letting the liquid disperse across the surface of the rooftop.