C.P.
You're definitely overreacting.
Bow-hunting requires that the game be very close, and the hunter be very accurate. Also, if you saw him last night, walking, it's not likely he was hunting at the time. He was scouting. Looking for signs of deer. Tracks, scrapes, rubs. If he was hunting, he'd be in the stand, waiting. And the stand is probably faced into the woods, away from anyone else's property.
Call the school if you like, but it may very well be that they gave him permission. Hunters do not usually put their stands and game cameras on private property without permission. It's likely that the school's property is being overrun with deer and they need this person to come in to cull that population.