They should go back to offside whether interfering with play or not. I know it can, very occasionally be frustrating when genuinely not interfering but just stay onside ffs. Cuts out all this other shite.
purely by being there, this guy was interfering with play, because Dave had to guess what an offside player was going to do. Aside from the fact that they could’ve had two players sent off and they repeatedly fell over and kick, barged... anything they could to spoil the flow of the game. The ref did his best to facilitate this. Deserved at least a point despite the awful 2nd half.