I get the technical ruling being correct. However he only had to go about half a metre, he wasn't tackled so doesn't have to release, and unless he lets go of the ball he has to use his knees to get to his feet - I would argue that he did this and the actual propulsion was from his feet. If, hypothetically and all other things being the same, he had to go 2 metres, and he used his knees to stand up and then dived over the line would it still have been a double movement? No way. In hindsight he had plenty of time to play it safe and release the ball, stand up, pick it up again and then fall over the line, but it's difficult to judge this on the fly when you are the player, you just want to dot the ball down.
It's rulings like this that have the leaguies laughing at the game.