Atmospheric friction is capable of consuming quite big rocks (thank goodness), so the rogue camera probably didn't come from space. And if it was identifiable at all, it probably didn't fall from very high.

I'd be looking for hang gliders or microlights, hot air balloonists or parachutists, all of whom obsessively document their activities on film, sometimes under slightly marginal conditions. And switching lenses while plummeting at 160 mph towards Earth is a recipe for disaster...

Was it a long lens or a wide-angle?