2 umpire mechanics

[Dakota]

NFHS varsity contest. Two very good teams.

R1 on 2B. Batter hits a hard infield grounder. F6 fields it. R1 running toward 3rd. F6 decides to throw to attempt to get R1 instead of taking BR at 1st. R1 does not slide, runs to the outfield side of F5, who takes the throw and attempts a swipe tag about 1-2 feet from the bag. BU has moved with the play toward 3B; is about 10-12' from 3B on the outfield side at the time of the play. Actual tag is hidden from BU by R1. BU calls safe. DC wants to discuss call. BU conferences with PU. PU says he did not see it, he was watching BR to first.

Please critique the mechanics of both.