Glitch
Write down all the possible moves of the pawn in chess.
Hint: You have learnt everything about pawn moves except for this one.
Anyway, in your second photo, there is an "i" symbol next to 5. dxc6. That icon can tell you what you missed out.
In short, it is a special chess move in which a pawn of yours (sitting on the fifth rank for White and fourth rank for Black) can capture an opposing pawn (on an adjacent file) which has newly moved two squares from its starting position.
This capture can only be made on this turn. Allowing this opportunity to pass would result in the en passant right to be lost.

