If it had been a landing, it would have been a splat.
I consider base jumpers crazy.... but sailplane guys think hang gliders crazy too, so there is actually a continum of disrespect. ( and all aviators think bungee jumpers drunk frat boys with zero skills.... )
Ground effect is dependent, partly, on wing tip vortices, and the span of the wing determines how high ground effect works. IF he was flying down a slope equal to the glide angle, you could notice some effect, but only at less than about 6 feet. Closer to 4. In the above video, he punches through any ground effect too fast for it to be more than a bump.
I think his planned fabric slope Vegas landing is supposed to take advantage of ground effect, but on the close fast passes over rocks, etc. not so much.