The vertical separation in that experiment was not the actual distance.
Even if it was, 100ft is not exactly a near miss in that environment.
Point is, with a drone it is a preventable element of risk.
I have yet to see one while working. Entirely possible they have been there.
Outside of maybe three wingspans to the front and one to the side against a solid background one would be hard pressed to see a drone.
Perhaps more if above the horizon.