That's exactly it, imo.
On the one hand, for most of them it's 'oh you made a mistake over there but it doesn't matter'.
In Nigel's case, was it last week, either Motsi or Shirley thanked him for not making mistakes...
. Certainly, at least three out of four of them last week used the word mistake, even in praising him.
I think last night they pretty much ignored all that was good, and went straight for the mistakes narrative with him, yet again. The only other one who has had similar criticism, on other nights, is Angela S. I imagine he and Katya came off the floor last night thinking they had done at least as well as some of the others, until all they heard was MISTAKES and then they ended up second from the bottom on the leaderboard.
So exactly as you said, you either give fair critique to all or none.