Both cannot improve something using moves, so they end the game. The game is played in alternation of the two players. Play is to be done with either a move or a pass. The alternation starts with black. Then each player makes one move.
Alternation proceeds for most time of a game with moves only.
Here black 53 is the first pass. White still can improve the points' colors with his move 54. This ends alternation and the game. Now the win can be determined. In the late stage of alternation white 1 is a pass.