The cards turned into a different color and move to the top right corner as they are closer to win a game, when the card turns red with the word winner it means that somebody won a game already, could have been 1 line, 2 lines, coverall or any other being played at that time, but actually it could not be you who won but some other player.

 Whenever you win a bingo game you will see a big pop up on the game screen saying the word Winner and with your username on it.