I haven't been able to find any online discussion which would elucidate further. Everyone else discussing it is, at best, at a loss to explain it. However, here's what I
think must have happened, from what I can see at
https://www.youtube.com/watch?v=lOaW-CpzXzo :
Wing official #40, near side (line judge, I think, from what I believe to be "L" on the shirt) sees the snap motion start, loses sight of the ball as it passes between the snapper's thighs, and next sees the ball emerging
late in the backfield. LJ
assumes something funny has gone on with the snapper's motion of the ball that caused it to be late emerging, blows whistle (which he already had in his mouth with his left hand on it), and goes for the flag with his right hand. Actually the ball was late emerging only because it'd bounced off the snapper's crotch. R and U
see nothing, but throw flags anyway, "confirmatorily". As LJ goes to talk to R, U starts to make a motion with his right hand to touch his left forearm; I've no idea what that means, and the director cuts away from that shot. FJ in the replay has both arms out and thumbs up as he looks in the direction of the ball.
R, who had approximately the view of the snap we get in the replay, knows the snap was legal but doesn't want to rule IW and give team A a free replay after their snapper so egregiously goofed. Therefore he upheld the snap infraction, costing them 5 yards but getting to replay the down, possibly a fair bargain.