Watching GMs play bullet can be fun, and Carlsen is crazy good, but in that clip Carlen's opponent simply blundered his queen in one. Based on how quickly the rook move was, it might have been a premove. Either way, the other guy just wasn't thinking.
Exploiting premoves in online chess is a common "dirty" way to win, such as when FM Lefong Hua plays Bh6 after his opponent plays g6.[1][2] Even Carlsen has been tricked by this, such as when GM Andrew Tang got him with it in a Lichess tournament.[3]