I just found this thread and although it's very old, I hope nobody minds if I revive it
I just read the StarLog you mentioned and it's really a nice spin on the "Two Martys" theory !
Here's a link on Archive.org to read it on page 70-72. The Two Martys theory we can find the most online is the one where Doc "kills" the other Marty - to avoid him going back and getting involved with our Marty's actions.
The StarLog article is based on the fact that we see a silhouette running in the back of the parking lot the moment Doc throws the gun down. They state that this is the other Marty coming back from 1955.
Our Marty jumps in the Delorean and vanishes to 1955 to save him/his parents and comes running the other Marty, throwing himself at Doc Brown but he's dead. No bulletproof vest. So this Marty goes back home, terribly saddened. But that's not all! He no longer has cool parents or a sweet 4x4! He has a skateboard, family issues and the occasional visit from a loud and drunk Biff Tannen.
How did this Marty come back and not change anything ? Well this article assumes that Doc didn't actually think in four dimensions and thought he had a good plan !
As we know - Marty has come to him for help in 1955, so he figures - alright so I sent this kid back so I got a good 30 years before he arrives. Problem is, he's gonna be born soon too, so I gotta make a fail-safe for this kid.
He knows exactly what happens in that parking lot from the videotape, so he simply tweaks it a bit. Hell he's gonna wear a bullet proof vest, so might as well tweak this right.
He explains to the other Marty (rich, 4x4 Marty) not to talk to anyone/touch anything and come back ASAP from any time travel. He sets things up and the Libyans arrive.
The other Marty goes back in 1955 but he's one HELLUVA driver because of all that 4x4 driving, so he avoids the Pine Tree and stabilizes the car. He drives to a nearby road, fills up the plutonium chamber (which Doc also made sure wouldn't be a problem this time around) and comes back to the beginning of our movie. And then spends the rest of his life thinking about his sweet 4x4.