I don't think so. I propose there are a couple of other ways that Eastwood Gulch could have earned its name than what you have outlined above.
Option 1. Remember Marty (aka Eastwood) had disappeared right after the train was stolen. That alone might have been enough to convince the town that he was the one responsible despite his earlier 'hero' status in defeating Buford "Mad Dog" Tanner. In fact, that could have played against him if people thought he was 'eliminating potential competition in robbing the train.' After all Buford and his gang had already robbed the stagecoach. A train might be the next target.
Doc Brown would have also had Clara as a complicit partner for an alibi. A respected teacher, Clara could have sworn up and down that Doc was not anywhere near the train at the time it was stolen. Thus, Eastwood would be blamed and Doc would be off the hook.
Option 2. Another alternative might be that Doc and Clara claimed that Marty acting as Eastwood actually tried to stop the theft of the train. He was successful in driving off the hijackers but unfortunately having been shot and died in the attempt. Having seen Eastwood fight off one gang might lead townspeople to believe he was heroic enough to fight another gang. Dying a tragic hero would be cause for naming the Gulch in honor of his sacrifice. One potential flaw to this option would be the lack of a body. Though, perhaps Doc and Clara could claim they buried Eastwood somewhere in private to respect his 'dying wish' to not be thought of as a hero just for 'doing the right thing.'
