this is an explanation of how the extreme landing on steep terrain came about and what the thoughts are. Further there are 3 variants of landings on the slope.
I had the same question in mind ... Since he was trying to use the thermal and the ridge to climb, I think he was probably in a very gentle tailwind on the waterfall, considering also that the wing overshoots him, but I would like to know how to consider the wind in these cases. Epic landings!
Another type of side hill landing you can do, only if you have good ridge lift. Is to get your wing to almost go parachutal, then you spin your glider so that it is facing the hill. Right after your glider is facing the hill your feet should be on the ground, catching your wing above you after spinning it gives a really nice flair
The first part on speed landing reminded of a documentary I had seen on a Swiss hang glider - Didier Favre - who was a pioneer of vol biv and who used a similar landing technique. It's in French but the auto generated and translated English closed captions are enough to understand: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-zrr0s85S6jA.html