dirtbike problems

me and my friend decided to go riding. We got all gassed up and such, i had my crf250x and he had his rm250. We were riding, probably about 15 minutes into the ride and my friends bike, he had noticed was running unususlly well. We didn't really worry too much because it was running well but we should've knew better. we were out in this field riding when i looked and my friend was stopped on the side of a tar road. His bike was off and then he whipped his helmet into the woods. Then he pushed his bike and ghost rid it into the woods. I asked what happened and he said the engine blew up. We pulled it out of the brush and tried kicking it over. Sure enough it was all seized up. So we pushed it to a road and had a friend come pick up his bike. We then went to my house where we opened up the engine and sure enough the piston head was shot. There were big chunks of metal broken off and we found a couple pieces laying in the engine.