And Kompanys challenge is not the sort of tackles which break legs, for that to happen one player needs to slide in, the other player has to stand with his full weight on the leg, so that the studs avoid the leg to move, and all of the impulse of the sliding player has to be stopped by that leg.
But that's not the case, because Kompanys foot did barely move forward, also his center of gravity. It may look from the side view as if he was sliding in, because the camera is moving along Wishere.
And yes, Scholes should have gotten a red card there