In the wikipedia article it actually says that there is a theory that his body was placed on a nearby burial mound and moved by the ice to the location were he was found but:

> While archaeobotanist Klaus Oeggl of the University of Innsbruck agrees that the natural process described probably caused the body to move from the ridge that includes the stone formation, he pointed out that the paper provided no compelling evidence to demonstrate that the scattered stones constituted a burial platform