Is it fairly common for the fastest runner at the school to not be on the school team or even on any team? I've seen this happen on several occasions:
School 1 (HS): Athlete in question had a disagreement with the coach (too much intensity, not enough mileage), ended up training on his own, and ran a modest 4:50 1600 that was still better than the rest of the runners on the school team.
School 2 (college): Athlete had lots of talent but was injury-prone and thought that the school's program was too intense. She competed unattached in the school's home meets and almost always beat the other runners on the team.
School 3 (college): Athlete was a grad student who ran out of eligibility.
School 4 (college): Athlete was a double engineering/business major who felt that he was too busy to join the team. But he somehow managed to run fast times despite having a rather strange and irregular training schedule.