Vortex ring? Don't think so.
If their airspeed was low enough for vortex ring, say 20kts and they travelled a mile after the start of the event (with the wind from about the half past one I think) then to travel that mile it's going to take them about 4 minutes. At the same time they dropped about 400' in that hypothetical 4 minutes ie 100'/minute. Hardly vortex ring territory.