You do see “him” flying in the air and emerging from the pool, in a continuous take.
You lose sight of him at the trough of the slide. A figure appears on the upslope of the slide, flies through the air, lands in the pool. Then you lose sight of the figure behind the pool walls and a man emerge from the pool.
So maybe there were two different men at the beginning and the end, and a dummy flying through the air.
On the other hand, it looks like it might be in Norway, and they have some insane people who jump off cliffs in wing suits.
I agree about the dummy/model part.
And the rate of acceleration down the slide is way too high. Looks like he had a rocket propelling him.
Look closer at the slide and the bumps/waves in the bottom third of the surface that we can see. At speed, a body in motion would go airborne. No air before the ramp that I can tell.