I have no idea how they came to that conclusion. The post on the PL Match Centre says Fernandez isn't offside as he didn't touch the ball, but him being there in an offside position certain impacts Martinez and arguably also the keeper. If Fernandez wasn't there Martinez could have moved across to Haaland, he's just said that himself. Also the keeper can't move across to better block Haaland as he has to assume that Fernandez might head it on goal. Plus, as has been said, it was very subjective so I don't see why there wasn't an on field review. Fully expect there to be an apology from Howard Webb.
No problem with the red card, its a clearly violent action to kick someone in the stomach like that. I didn't see anything that Fernandes did that could be classified as using excessive force or brutality, but it is poor that he wasn't cautioned.
Also, Michael Oliver was hit by the ball four times in this game. Wonder if that is a record, I can't remember seeing that happen before.