"throwing a piston" is more of a figure of speech than actual physical occurence. For an aircraft engine to throw a piston the cylinder would have to effectively be ripped off the engine to expose the piston and or conrod. It certainly is possible to break off a cylinder at the studs (very common in certain engine types) and this would explain how the aircraft was able to continue with the circuit.
If this aircraft is under water as has been suggested I am impressed with the quick recovery, engine failure analysis and dissemination of information to pprune.