From what I remember of the red card, Moore skinned Robertson (not for the first time) and Robertson took a frustrated swipe at him as he went past, but missed. Bizarrely, a couple of years back when playing for Queens Park at McD, his namesake Andy Robertson was sent off for exactly the same thing in almost exactly the same spot on the pitch!
I suppose even though they both missed the player it is technically violent conduct, so the red card was probably correct. I once had an opponent sent off for something very similar in the Dundee u18 leagues, although he did try to elbow me in the head as i went past, as opposed to kicking me!