Yes, 50-minute exposures would certainly rule out geosynchronous; I've used image stacking to look at geo and you get visible movement relative to the star background after even a few seconds. Fifty minutes would be almost 15 degrees of movement relative to the background! This isn't even accounting for the fact that you would need to be looking in a narrow region above above the equator to get something geosynchronous to begin with.

There are other possiblities that are likely: Upper atmosphere tests resulting in transient luminous phenomena. This would be more likey in certain conditions where the sun could reflect off of specular matter (e.g., bits of metal). You would see this most likely within 1-2 hours of sunset or 1-2 hours of sunrise (source: I've used optical equipment to spot satellites professionally).

I'd note that thier pipeline for removing "plate defects" is not based on the PSF but on some vaguely defined "expert review" training. This can, and should, be a quantifiable step.