He faked injury and wanted to come off because he was nervous and probably wouldn't want to be the cause of them losing, then he suddenly decided to grow a pair, probably realised penalty shootout makes heroes out of keepers so he wanted to stay on. That is my arm chair psychoanalysis of it anyways, but it could sort of explain why he refused to go off, like a maniac and why the manager exploded when he sensed some weak ass bullshit going on from Kepa.
Kepa celebrated like a madman way over the top after his save. Ref had to tell him to leave right before Luiz missed his shot. Weird bunch. I hope we get to buy Kante from them, would be nice. He doesn't belong there.