Car engine failure

I was accelerating in my 2015 Chevrolet Caprice Royale In the M mode and I shifted From 2nd to 3rd while the car was on 6000 RPMs and the engine failed and some type of white smoke was going down my exhaust I quickly pulled over But the car wasn’t starting again it also leaked a lot of oil and water and I saw the piston Rod on the floor (which was clearly broken form my car) now the mechanic says that the engine needs an overhaul which costs around $ 5K… whats the main reason for that ??