I hate watching injuries, so I won't be going back to have another look to confirm what I'm saying here. But it seemed to me that the ref blew his whistle to stop play very quickly, well before the Penrith players had made that break down field. For him to have blown his whistle that quickly, he must have made his decision to stop play within a second or so of Oates hitting the ground. At that time, Oates was out cold laying next to the ball, undeniably a dangerous position on the field. Stopping play is 100% the right call.
In addition to that, Penrith ran 10m or so and threw a pass after the whistle had been blown, which made it look like they were in for a try. If they'd stopped at the time the whistle was blown (and I don't blame them for picking it up and running, it's a footballer's instinct when they see a loose ball) I doubt we'd even be having this discussion. Play really was stopped very quickly.