It's Silfir's Chess Accuracy Corner! Rating depictions of chess based on their accuracy since sometime before now!
Unfortunately, it was painfully obvious the artist had no actual knowledge of chess. They kept to long-distance shots, or an extreme close-up of the bottom-right corner on the board, but still managed to pack in two errors.
- The board is set up wrong by 90 degrees - the bottom right square is supposed to be a light square. Dead giveaway.
- I'm not 100% certain since it's mostly obscured by a speech bubble, but based on the round head and the relative size compared to the rook it appears there is a white pawn on e1, which is obviously impossible. If that particular panel is a close-up of the checkmating position, which is implied by it getting the focus following Sieg's declaration of checkmate, that would make the black piece the king. While there are a number of valid checkmates to a black king on f1 that could involve an unknown white piece on h2 (possible a knight offering check), a rook on g3 and an unknown piece (which cannot be a knight or a pawn by the rules) on e1, as well as any number of other unknown pieces - in all of those imaginable positions it would make no sense for Ritzhardt to express surprise at being checkmated unless he is very inept at chess. Surprise one-move checkmates CAN happen to good players, but not like that.
To be fair, this is a completely casual setting, and it has never been suggested that Ritz is any good at chess. They just enjoy each other's company.
So, as an aside unrelated to this particular instance of chess use in fiction: Chess games ending in a player going "Checkmate!", with the opponent stunned by the brilliance of their opponent (rather than their own stupidity for missing it) is the chess world's equivalent of hackers furiously typing on keyboards, or showing a player is brilliant at poker because they keep getting four of a kinds or royal flushes. For anyone curious, the correct way to demonstrate brilliance is to have a chess player sacrifice a piece (or do something else unexpected or outrageous, but it's usually piece sacrifices that players are liable to miss), the opponent's eyes going wide, and frustration washing over their face as they calculate ahead to see how completely and utterly screwed they are. Or, quite possibly, a player announcing "Checkmate in six moves", simply because a combination that involves calculating multiple moves ahead, with all possible responses, is much more likely to have been overlooked by even a good player. The amount of moves has to be balanced; "Checkmate in three" is not impressive enough, "Checkmate in thirteen" suggest either computer cheating or the player being an absolute freak of nature. Think Magnus Carlsen.