This is probably a good time to enlist the expertise of a more experienced electrician.
Your friend has caused a problem that could be inside a wall or ceiling and has the potential to be very dangerous, this is not the type of situation to be learning how to repair or use test and locating type of equipment on an internet forum.
Roger
I would say the friend has exposed an existing problem rather than causing a problem. A short like that shouldn't cause severe damage if the circuit is protected. If it was bad enough, I would think the breaker would trip.
It might be a loose wire on a receptacle. I would guess another light but I can't imagine they would hit a light in a room further from the panel then come back. It might make sense that they hit a receptacle in the room before the light. But you never know.
Also, if the OP did not verify the breaker was off, how safe is that?
Speaking of breakers, maybe there is a different panel somewhere in the house. I find a lot of panels in old houses that used to be the main panel that are now being sub-fed from the new main panel.
PS to the OP: Think about what would happen if something was "off" because of a loose wire. Then suppose you started working on it and jiggled the open connection back to a closed connection with the wire in your hand. Be safe.