There's no way you can lay the blame at Walker's feet. The ref has called the captains over with the specific aim of telling them to calm their players down after constant handbags. In that situation, you should be allowing the captains to then go and share that message, as they do in rugby, or at least stopping the play until they were back in position. Walker passes the message on but is assuming the ref will wait until he's in position before letting play start, and he was right to assume the ref would do so. I'm certain the referee regrets allowing them to capitalise on that situation.