What happened?

I went golf today. My golf game has been going very well until the 17th hole, but the accident happened on the 18th green. By 17th, my score was 11 over which was so good to me. If I finished for par at 18th, I could win today's game and I would get about 10,000 YEN. On the green, I hit the ball with concentration. After I hit it, I realized that the other player's ball was near my ball, and finally my ball hit his ball. According to the rule, that accident gives me 2 penalty. In the end I was ranked the 3rd in today's competition. After the game, I advised the other player who didn't mark his ball at 18th green that he should mark his ball as soon as possible when his ball was on the green. Can you understand this topic?