The victim lives with his mother in the shooter's other property. Presumably they were known to eachother.
The shooter and victim had a convo. Shooter left, went home for his gun, returned and killed the victim, while he was showering. The shooter did not call the Police.
No telling what was going on, based on the inf disclosed thus far.
Belfair homeowner arrested after intruder fatally shot while taking shower | The Seattle Times