Technically it is a shoulder charge, but I think the issue is that nearly everybody agrees there's nothing wrong with it. The problem with the shoulder charge rule is that in most cases the shoulder charge isn't dangerous, and often used by a defender trying to protect himself from a big collision. Plus there's already a rule to protect players who cop a shoulder to the head. That merkin smashed by Kane Evans last week was hit in the head by Evans' chest!
I think it was a great tackle - and I'm a firm believer that he, as a last line of defence, should have the right to do it to prevent a try (as long as he doesn't connect with the head, which he didn't).
But shoulder charges were banned, and the on-field ref picked up on it - but the Bunker refused to make the right calls imo.
I think Ponga's tackle was fantastic - but by the laws of the modern game, it was a penalty, and even a possible binning.