Well actually, i would say its neither. The root problem is that the refs are seen as infallible, so once a decision has been made in the game its done and dusted and not open for further action. No doubt Oliver and Tierney made the wrong call there, but if it was possible to overturn their call there are retrospectively punish Pickford i think people would be a lot happier.
Now of course wrong and decisive calls in matches cant be undone and its not like the match is going to be replayed, but if the FA could admit their refs made mistakes once in a while it would be a lot more palatable for the rest of us. For example the Martial/Lamela incident feels bloody unfair because what Martial did was no worse than what Lamela did. The difference is that the latter managed to con the ref by acting like a cnut. Now the sending off is in the past, but really, either Martial should have his ban lifted or Lamela should have faced similar sanctions
The whole thing is so incredibly daft. In any other walk of life, blatantly wrong decisions can be overturned, but not in the EPL because apparently the refs never makes mistakes there