I think they got it right and you can play the ball to yourself, even if the commentators don't think so. You just need to get behind the ball before you do so. Nightingale got a foot behind the ball before picking it up so he was free to play on.
If that isn't right, the only other option could have been a Dragons penalty for interfering with the play the ball IMO
I thought the same as the commentators, but I had a look at the rules and your first call appears to be right and it seems you don't even need to get behind the ball.
NRL Rules Book said:
Play with foot
10.(e) When the ball touches the ground it must be heeled (i.e. backwards) by the tackled player. The ball must not be kicked or heeled by the player marking him.
The ball is in play when it has been played backward.
It seems any player who isn't out of play can pick up the ball once the ball has been heeled backwards. We see this when the tackled player expects the acting half to be there when he plays the ball, only to have the marker swoop down on it and regain possession because there's no acting half. You could even heel the ball back to another a team mate who isn't at acting half.
If we assume for the sake of argument that the play the ball wasn't complete when the ball hit Halatau, then your other interpretation is probably close enough for most people, but after the reading the rules I'd say it's a scrum, due to Halatau's interference being unintentional.
NRL Rules Book said:
Penalise intentional interference
10.(g) If the ball is played quickly, all players will not necessarily have time to retire the prescribed distance. They should be penalised only if they intentionally interfere with play – either actively or passively.
Accidental interference
If the interference with play is accidental, a scrum should be formed. Interference should not be considered accidental when the player concerned has had opportunity to remove himself from the area in which play is taking place.
Finally, I'd say the only part the ref got wrong was when he restarted the tackle count. Halatau didn't play at the ball, so it shouldn't have been six again. In the end it didn't matter because of the Naiqama intercept.