It's not that impressive at all, Liverpool also were not as impressive as people make them seem really.
They transitioned well and were clinical. If it was Ugarte not Casemiro, different story.
Ugarte releases the ball quickly when he wins it and doesn't lose the ball, so 2 goals were down to him. The other part was not clinical at the other end.
We're supposed to transition, so Liverpool got the ball and didn't lose it on the transition.
United lost it when the full backs were in transition going up the pitch, Casemiro dithered on the ball and lost it.
It wasn't that "Uniteds full back were high up" it's that United had the ball and Casemiro lost it in stupid positions.