There are at least two threads about this at the Ed Forum, and Steve Roe has a good piece on it.
Notwithstanding the "odds," it's a coincidence.
Martin was a 17-year-old kid whose father was a minister of some sort. He was a teenage right-winger who emerged from his time in the service as a pacifist.
I fail to see how your suspicions make any sense. If he had the knowledge you suggest, why on earth would he have turned over the film to the FBI? Think.
I'm a bit troubled by him saying the film is the one returned to him by the FBI in 1964 when it dates from 1977. It's such a weird pastiche of images that I can't imagine what the teenage Martin was doing. The Walker-Oswald images are completely inconsequential - what purpose would they have served in whatever plot you are suggesting? Think.
I have written about synchronicity (seemingly meaningful coincidence) because I've experienced so many complex, jaw-dropping instances myself. Some I would describe as "impossible" - but they happened.
Assign this to the same category as Umbrella Man - weird sh*t, but irrelevant to the JFKA.