There's one way I can think of that would prove conclusively whether the Armstrong jump was running forward or backward, but it depends on two critical questions.

1. Did the jump occur from the lunar surface, or from the footpad?

2. Are Armstrong's feet in view?

If the answer to both is "yes", then if the footage was faked, there should be a plume of dust flying out of nowhere before he touches the surface and meeting his feet as they hit. However, if it's not faked, any dust plume should fly off as (and after) his feet leave the surface.

I doubt there's enough resolution in this footage to see this particular detail. But my point is, even though one ballistic trajectory is much like another (forward or reversed), there are second-order effects which might give away a fake... or prove that no fake occurred.

It would be fun to run the "Armstrong jump" backward to see if there are any apparent discrepancies.