Very poor gamesmanship
To admit it publicly surely raises the question of whether the result should be reversed?
Bringing the game into disrepute etc
Nah. Also he didn't admit it publicly, he admitted it to a mate who then announced it.
It's done, it's over, we wuz robbed, no blame attached to Sinckler. It's like walking in cricket - great if you do it, but it's up to the umpire to make the decision. Seen plenty of tries scored by teams I support when the player actually lost control of the ball, etc.
The AR obviously and clearly lied about seeing the grounding and given his other errors I suspect he might quietly get binned off for a while, or be asked to do some more training. That's all that'll happen, and it's all that should happen.