Law 10.4 refers to a tackle. It wasn't a tackle as regardless of the outcome or how well he did it, he was contesting the ball.
It's Rugby not AFL.
And it's not a penalty because he did not break the laws.
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He didn't make it to the contest for the ball though. He arrived there after it was well and truly over.
If you want to take a dim view of his actions you can say that he both took the player out in the air and had no arms in his tackle.
I wouldn't take that view because I think his actions were careless rather than anything more sinister however it was certainly a penalty offence.