Sometimes the excitement of a big event can make your body basically forget it's injured.
Couple of years back I managed to get a horrible graze on my ankle about 2 days before the Auckland half marathon - hurt to buggery and could barely put weight on it. Come race day and managed to smash out 21km at record pace.
Obviously not quite the same as playing an NRL finals game but I can sort of see the logic. There'll be tests in place to establish whether the body is up to it.
Graze different to soft tissue injury.