Bizarre ending to HS football game

The first thing the coaches should have stressed at practice is "play to the whistle." Did you hear a whistle on that play? So why did they stop playing? I covered a game last year where a punter shanked a kick and it went only about three yards past the line of scrimmage. All the linemen on the kicking team began walking off the field. One of the linemen on the receiving team can now say he has a punt return for a touchdown.