I own a used 1995 Toyota Tacoma. While cutting down trees on my property in northern British Columbia with an electric chain saw, my wife and I were startled when the truck, parked about 20 feet from where I was working , spontaneously started. There was no key in the ignition and no one within several miles of us. I ran into the house and got the key, put it in the ignition and turned it off. I called my brother, a biomechanical engineer who retired from GM. He had never heard of this happening. It never happened again. How could this happen?
I suggest you go the “paranormal route” (like the movie) and keep a camera trained on the truck and document these kind of things. Really all people can say is your wiring harness is damaged (or ignition switch) but no mechanic should be criticized for not being able to give a difinitive answer here.
Either you have a remote start system and while you were bending and man handling wood some how the button on the remote in your pocket got pushed (happens every now and then to my dad). Or I have to say its very very hard to believe. I have never heard of such a thing before.
The key to the truck was in the house, and there is no remote starting system of any type that I know of. When I bought the truck used, I was given two keys with a remote door lock attached to one of the keys. The door lock was attached to the key in the house. The truck hadnt been driven for about 24 hours. Im a researcher and dont believe in the paranormal, so I believe there has to be a logical explanation.
It’s a Toyota.
Ahhhh…well, the good researcher can’t cross things off the list until they are completely falsified (which mostly doesn’t really happen for all serious questions). The lack of definitive evidence can’t falsify…so… 
I suppose it is possible, since you bought the truck used, that it has a remote start that you don’t know about. (That is a verifiable/falsifiable claim). If it does have one all it takes is the stray, random signal of which there are plenty flying around these days.
I suppose it is also possible for some weird ignition wiring issue to do this. But I don’t know how.
Just to rule it out, when you put in the key to turn it off, did you just turn it from Run too Off/Lock, or did you first have to turn the key to Run?
“Do not struggle against the inevitable…” Wasn’t that the opening line for the television show OUTER LIMITS?
I don’t remember if,when I put the key into the lock,if it was in run or lock position. I should have, given what I do for a living. The only thing unusual about this truck is that the former owner had installed a CD and a special radio in it that I still haven’t figured out How to use. As part of the system he also installed a small antennae on the windshield.
I have got it. The previous owner installed a “come home” package in this vehicle. It is merely trying to find its way back to its owner. The owner had to have a microchip implanted somewhere in his body (battery changes are tough) and the car finds him with that special radio and antenna.
Some years back, I remember a call to “Car Talk” where the caller had the same problem you have. I don’t remember how Tom and Ray diagnosed the problem, but they had a car that tried to start by itself while on the lift in their garage. I think it might just be possible that a bad starter relay or solenoid could not only activate the starter, but backfeed power to the ignition system.
A remote starter that was installed by the previous owner and somehow kicked off sounds like the easiest solution. I had to drive a new work van, and just because I am a curious guy, seeing some strange button, with x2 on it I pressed it twice. The van started all by itself without a key. I put the key in the ignition and tried to turn it off, no luck, Like a monkey at the typewriter I finally hit the right combination to turn the engine off on the fob. I am reminded of one story here that the guy did this remote start thing, left his remote on the kitchen table, and could not turn the car off.
Hope it never happens again, but prepare for the future.
I have seen several cars spontaneously crank when the starter solenoids or relays failed and an older Ford actually was running with the starter engaged due to the wiring system. But for a car to have the ignition on and the starter crank the engine until it began to run and then the solenoid release is way too bizarre a set of circumstances. Only the presence of a remote start system makes such an occurrence plausible.