I realized that “out of form” is a relative term.
I think that Caruana, in particular, benefited from his pre-match prep, whatever it was. If the Caruana of one year ago had played the Carlsen of this year, he wouldn’t have finished with an even score. He must have gotten better.
Getting better, not so much being good, is important. This is what I had in mind when I posted something earlier about getting better at rapid time controls. Caruana has shown that when he puts some labor into getting better at slow time control, he can do it. So, he should also be able to do it at rapid time control. (Of course, meanwhile, his rivals won’t be sleeping, either.)