I kind of bet we'll hear it was a large amateur rocket, whether that is the truth or not.
Unless the perspective was deceiving, that rocket didn't look amateur to me. Most amateur rockets go more or less vertically (just because you don't want to have to walk a few miles to retrieve it). The rocket in the video appears to have a significant horizontal component (especially because it appears to have changed direction at one point, but perhaps there was some bad windshear). IMO, it was either a badly screwed up (but rather powerful) amateur launch, or the perspective is just screwy, or it's shopped, or it's not amateur. Who knows?
