Back me up here guys

[ChickenOfNC]

Had a seemingly straightforward play last night in a JV game:

A82 is split wide to my Linesman's side (I'm the LJ). A82 is set as a back. He then goes in motion, up to the LOS and then parallel toward the TE, then the ball is snapped.

Linesman has a flag for illegal motion.

I cannot get it through the L or the U's head that this is perfectly legal. The bottom line is, there are no restrictions on motion for a back other than he not be moving toward his line at the snap, correct. They are hung up on the fact that he is in motion on his LOS. This restriction only applies to a player who went in motion from a position on his line, who would have to be 5 yards deep at the snap, correct?