That was my point - Rafa doesn't tolerate players not doing exactly what he wants them to do. There's no wiggle room with regards to "he thought the short pass was a good option there". And the fact is that Rafa blames Mbemba for the midfield giving the ball away in that game, because even though his passes went to feet, they went to players who then turned it over and, in Rafa's plan, they should never have had it in the first place.
This was reported a few weeks ago, pretty sure in The Chronicle. It fits with what we know about Rafa, it fits with what we saw in that game. Rafa had a plan, Mbemba didn't follow it, we lost, Mbemba doesn't play again.
Probably compounded by the fact Mbemba was fucking useless all round that day, to be fair. And the fact he's simply not Rafa's type of CB.