Hitting another aircraft. See the psa flight that went down in San Diego years ago, they even have a few pictures of it after the hit and mid air fire.

No, there isn't. And an engine fire does not cause an airliner to crash. We all train those every 6 months in the simulator, if you get that wrong you'll fail the sim check and not get back to flying commercially until you've done remedial training and a satisfactory check fight.

So there is more to this crash than just an engine fire, or simple "pilot error"

The pilot failed to successfully evade an incoming missile?

> Is there actually any kind of believable “pilot error” that can cause a passenger 737-800 to catch fire in the air and crash?

Yes, here's one (on an A300) where pilot error while operating the rudder sheared off the vertical stabilizer and caused a crash:

https://en.wikipedia.org/wiki/American_Airlines_Flight_587

There were reports of an explosion/fire in the air, as the plane pulled itself apart.

> The crash was witnessed by hundreds of people, 349 of whom gave accounts of what they saw to the NTSB. About half (52%) reported a fire or explosion before the plane hit the ground. Others stated that they saw a wing detach from the aircraft, when in fact it was the vertical stabilizer.