In this game, Black (Go4TheEyes) got into a spot of bother on the left side, resulting in him making sequential atari to try to retain centre access. At this point, White should’ve extended to A, leaving Black to fix at B, after which White might want to enclose at G3.
However, he actually played the mistaken atari C, provoking Black to capture at A and form a gorgeous ponnuki. White even passively took the two western stones instead of resisting with the counter-atari.
As luck would have it, White also responded to the gote connection at A with the unnecessary B, allowing Black the key point at F4 and a very comfortable opening.