Car quit running while driving

Yesterday when I was getting on freeway my car would not go over sixty mph and then it was making a rough sound. I got off on the next exit and my car quit running on me. I tried to turn it on and it would not turn on. I popped my hood and all the antifreeze was coming out from the top and the bottom of my car. I put water in it and I pulled my car home. I was told it was the thermostat so the mechanic fixed it and it kept running really rough to he said it was a piston.