Those involved are indeed very powerful. Anyone else, other than students, might have turned him in. None of the dangerous creatures that lurk in the Forbidden Forest are in sight, and it is eerily quiet. Which brings Severus and Remus to conclude that a ward is probably being used to repel the creatures. And the potion, Regulus is still holding, could be used for anything, really, but the most likely thing is eliminating the competition.