Why did my Ford Escape 01 burst into flames while it was being towed?

The Backround information, my vehicle started to slow down and like couldnt build speed. I was only going 40 and running at about 4000rpm so I pulled into the TA that was just about 200 feet down the street and it turned off as I pulled in. So I let it sit for a few mins turned it back on and parked out of the way in the truck stop. Then I called my insurance company and they sent a tow truck. So we're go about 100 feet and the driver see my car trying to turn, he forgot to lock the steering wheel, so he fixes it and everything is fine for the next 16 miles, and all of a sudden my car bursts into flames. The engine wasn't on but the key was in it as the car was in neutral. The key was partially turned(don't know why he left it that way, prolly to stop the alarm) but that shouldnt make the car burst into flames. We're both fine, we were able to disconnect and get away from the car. Car is totaled.

Added (1). It was automatic, uh two of the wheels were on the ground and it was in neutral with parking break off

Are you talking being flat towed (all 4 wheels on the ground)? And is the car an auto or manual? It can do severe damage to the transmission if auto but I have never heard of it getting to the stage of the car catching on fire. Or if the park brake was left engaged it could get hot enough to catch the rear brakes on fire, though once again pretty unlikely. If it was neither of these unfortunately it would probably be an unrelated problem

See the source for NHTSA investigations of the 2001-2004 Escapes for engine compartment fires caused by bad connections to the antilock brake module.

I wonder if the reason you broke down was because of a serious failure in the transmission? Failed bearing or similar? Then when the vehicle is being towed the transmission is being turned over by the wheels. Grinding up what's left of the failed bearing until it got hot enough to set the transmission fluid on fire.