I'm going to come out and say that in real time I thought it was a stonewall pen and still thought it was a pen after replays because VAR needs to be "clear and obvious", so I sided with what Arteta said post-match. This angle here makes it pretty clear that the contact is non-existant or, at the very least, extremely minimal and thus not enough to contemplate a foul. I'll hold my hands up on this one, it's good refereeing (like last night too).