"Airframe rattling" with torsional motion of the engine on the pylon (what you called "auto-gyration") is consistent with a compressor surge. Surge can be caused by ingestion (the bird theory), failure of the turbine section (leading to no power to drive the gas generator), or off design operation of the throttle (not likely). It would also explain the "puff of smoke" seen by one observer, and any loud "popping" noises, since the mixture ratio in the burner goes rich (so it just starts a fire, instead of the standing flame front normally created).
Surge isn't necessarily accompanied by wholesale failure in the engine. So, the engine might still be intact. Depends on the cause.
Would it lead to the explosion of the wing? Probably only if there were an uncontained turbine failure (hot blades hitting the wing which is full of fuel), or if the torques caused the wing to fail, leading to sparks and fire etc.
By the way, pylon retention shear pins are normally designed to fail under loads considered dangerous to the airframe. The airplane flies just fine without an engine, but not so good without a wing.
But both engines and the tail section, like all together??? It does appear the tail section flew off first cause of where they found it.