Spark Plug Implosion
I had a similar, yet different situation. See the thread on the flashing check engine vs. static. My wife was driving, and the check engine light started flashing. She kept driving (bad idea) into the repair shop. There was a loud "pop" and the spark-plug had melted into the cylinder and fuel injector crapped, etc.... Long story short, we believe the spark-plug was loose, which caused spark to go past the threads, into the fuel injector, and led to an ultimate melt-down (exactly similar to your engine failure).
If you recently had your spark-plugs replaced, that may have been the source. Regarding repair, dealer initially declined the claim on our extended warranty, and when I really raised cane, they found the failure was the engine head, which led to the other stuff above, and the failed engine head was under warranty.