Chess.com, too, give us the facts, but not, in this particular instance, the story.
So what is the story?
Let Matt Fletcher tell us.
Hang on, what was that again? Black tried to reply to Rf8+ with ...Kg8?
How very odd. They're adjoining squares.
Let's look at the position. White checked on f8...
....and Black somehow moved his king like so...
under the impression that it was a legal square?
I think we'd better look at some footage.
The move itself occurs at 1:18:20, and the commentators miss it (which may help explain why everybody else seems to have missed it, save Matt) but as you can see, nothing particularly exceptional goes on - except that Black moves his king to a square where it remains in check. Given that the square is adjacent to the rook, it is very strange indeed that he did not appreciate this.
Why might he do this? Well, who knows. One cynical suggestion might be that if you're down to a few seconds on the clock and you don't know what to do, you might appreciate the extra tme you get while the arbiters are restting the clocks, and never mind the opponent's added two minutes. And the g8 square is really not very far away from the rook on f8.
A kinder suggestion would be that it's a sporting situation of very great stress, and mad things sometimes happen in those situations. (I'd cite, for instance the Korchnoi game mentioned here, or the Geller game mentioned here
in which Geller thought that he had 68 fxg3+ followed by king takes rook.)
Certainly that's how Rodshtein tells it.
You can make up your own minds. But perhaps it's lucky that Fedoseev won the game. Otherwise, we might have heard a lot more about this incident than we did.