Just rewatching the game, and I think I can see what happened.
We played the first 22.5 minutes in a high pressing 4231, then the middle 45 minutes in a low block 451, followed by a bunch of substitutions and a return to high pressing.
It didn't look as bad on second viewing. I think Ole just wanted to test a couple of things out. Hopefully we won't try it again, though Matic and Pereira in particular made things considerably worse than it should have been with their general ineffectiveness.