I don't blame Spigen for trying to take credit for this, but the phone's survival was probably 0.0001% attributed to that specific case. From 16k ft, the phone would've been at terminal velocity for a good while, so probably little difference between that and a not so impressive sounding 200ft fall (or whatever is needed to reach terminal velocity). Judging by the photos, there were trees and a grassy area beside the road, with the NTSB investigator paying particular attention to the trees. That suggests the phone may have fallen through them, slowing it down, and landing in the grass. The road and phone are also wet, along with dirt/mud pressed into the case (shown in a photo), which suggests recent rain that would have softened the dirt and further cushioned the impact.
That phone would've survived with any sort of case on it in that situation, maybe even without any case at all. It was pure luck that it did, and Spigen is just using the sensationalism as a PR event.
Though if Spigen wants to drop a covered phone from thousands of feet onto something that matters, like pavement, then I would be impressed if the case protected enough to survive it.