Seems pretty odd. Particularly given a referee can issue a card when the game is over.
I had an strange one a few weeks back. We were up 1-0 with 2 minutes to go. I scramble to clear a ball that was centre field in the middle of my own half, the ball goes well out of play but not too far (I hit it with my weak foot) and the receive a yellow for time wasting. Up until this point the referee had hardly used his whistle.