An NPC in Celadon Department Store 'moonwalking'.
The NPC moonwalk glitch is a minor natural glitch in at least Pokémon Red and Blue.
If the player presses the A button on an NPC one frame (i.e. 1/60 of a second) before they turn, depending on the NPC they will either immediately turn before chatting with the player or appear not to turn. When the player then closes the dialogue box, the NPC will walk backwards instead of turning.