I have a lot of sympathy for the appeal case. To me, much the same argument was clear at the time.
Palace had a counter attack opportunity with a player sprinting into acres of space on the right if Mateta could poke the ball onwards into that space. The pass was played behind him, so he spun around and threw himself towards it in the hope of getting that touch. He didn't see Van Der Ven coming at the moment he launched himself.
I can see why they decided red, but to me Mateta was unlucky overall. The really irritating thing is that the best ref we have, who was up with play, aware of the context, and had a feel for events up close, thought a yellow was sufficient. Once VAR gets involved he's never going to overrule them, but VAR pays no attention to context, intent, or anything else in the real world, only close up slow motion replays.