Black blunders.

https://www.chess.com/analysis/game/live/120596425161?tab=analysis&move=40

[Edit - I forgot to mention it's a speed chess game.]

After 21.Be3+ black resigned. As you can see from the eval bar - the position is favorable to white so black blundered by resigning early.

He must have made the mistake I did in my head. It's not surprising I made the mistake. But it is kind of funny that a GM would "see" what I saw. He entirely missed the simple 21...Kc7. He thought he was forced to play Rc5 and then he's down a rook after white takes it.

Kc7 isn't much fun - ideally you want your king on the 8th rank behind your pawns - but it's not horrible for a GM. They are great at defense after all.

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The right sidebar had something I've never seen before. It has no number for black. I've seen 0.1 seconds but never nothing.

I assume white's move and black's resignation were within 0.1 of a second of each other so the site interpreted that to mean they happened at exactly the same time.