I could believe that gait/pace/posture vary by culture, region, and era... as with say diction and relative prevalence of different facial expressions. Even if you removed the cues of dress and surroundings, you might be able to watch video of walkers from different cities and tell New Yorkers from others, or at least large cities vs. small towns, etc. And just seeing how much more formally dressed city dwellers once were, in public - different clothes require a different style of motion and imply a different intended presentation to others.

But, I suspect artifacts of the filming and conversion to modern formats are larger factors. Slight differences in replay speed, or cyclical variations caused by either the original machinery or compromises of framerate conversion, could also lead to the kind of 'alien-ness' we perceive.