They stopped the game for the VAR check
Do you really think the ref would say that though? How stupid would an official need to be to admit that to a player knowing that every word he says is being heard by the lino's, 4th official and VAR (are they all in on this big conspiracy?) and very likely that his words would have been picked up by one of the countless Sky cameras?
The fact that Utd have very quickly came out back tracking would suggest that Shaw either genuinely did misunderstand what was said or he was twisting words.