There isnt any law that says you have to let a player get to his feet, for some reason a lot of people still play it. Otherwise you could just lie on the floor indefinitely. If a player slipped over when he was carrying the ball, you'd tackle him, the same applies when someone slides to pick it up
Are you seriously begrudging players the right to celebrate how they want to with their team-mates?? Absolutely ridiculous statement, it has nothing to do with football at all
Pause the video as Tuifau shapes up to tackle; at this point his shoulder is level with Robinson's chest and he's just trying to make a big hit, you can see his arms coming round. Robinson is falling as the tackle is made which meant it was high, it was a bit clumsy and nothing more, shit happens