3600 meters altitude is pretty unlikely for a quad (with a hacked DJI or a DIY quad you'll burn the entire battery climbing that high, so you can be there for a minute maybe, and in that minute you hit a plane? XD)... but these days everything is caused by drones, even if they don't see the drone, it's a drone, always, no matter what ¬_¬U
Probably a bird, or maybe a ballon like those you use to put DIY weather stations in orbit... or a fixed wing, like a modified parrot disco, but pretty unlikely. Crashing mid air is not as easy as crashing in a bidimensional plane like a congested road.
Drone crashes at low altitude near the runaway?... yep, like the other day with the canadian policemen.
Drone crashes over wildfires? Yep, planes and copters flying low on a congested area, pretty likely to hit a drone recording the fires because they'll share lot of time in the same volume of airspace (50-120m)
Drone crashes at 3600 meters? Let me doubt that.
We even had a policeman a few months ago going after a "rogue drone" that was actually Jupiter... yep, the f* planet. Drones, drones everywhere ¬_¬U
Drones are an extremely marginal hobby, just like RC in general, and it's not going to change... so don't expect dronestorms anytime soon XD