Didn't think it was a red personally. Doesn't catch him with his studs, and the slip is what made him catch him high up the shin. I think the desire should be to try and keep the game 11vs11 whenever possible and there wasn't quite enough there to warrant sending him off. Ref should use a bit more common sense, give him a yellow and a stern talking to.
That said, (1) as others have mentioned, Fernandes is a cunt who spends all day getting up in the ref's face. You can hardly blame them for wanting to send him off. (2) Fernandes isn't going for the ball; he's trying to take Maddison out to prevent the counter attack.
Yes he slips but that's what you get sometimes for making a dickhead decision that goes wrong. Only has himself to blame for giving the ref a decision to make. If it happened to, say, Romero, I'd be annoyed but mainly at Romero for being such an idiot.