What he said ^^^
Having watched the video a few times, there’s nothing wrong with the skirting of the cloud initially, as they have a clear route out into a valley. One does wonder why they didn’t do some tacks in the lift to get above the cloud layer but I suppose that would have made it too easy.
When they turn left, it sets them up for a bad outcome, but they still had the ability to do a hard right and exit for quite a while. What I find incredible is that there don't appear to be any blind flying instruments in the front and judging by the unusual attitudes, in the rear as well. Even if they were in neutral air, it appears they would have gone into cloud, which leaves a huge ??? hanging over the whole thing. From the comments on the official NZ gliding site, it seem like one of those distracted instructor, unsure student scenarios where no-one really has projected the flight path forward.
If you’re going to flirt with cloud, you need a plan to get out of it, should the worst happen. Having some kind of reference is crucial as you will disorient pretty quickly, especially in turbulence. There are also occasions where, despite the best of planning, the weather changes and you have to do a cloud descent. If you don’t have any instruments, you can do it on GPS (or even a compass) but that requires a bit of skill and mental discipline. Better to have a phone app for emergencies - I use iBFD in case of a double failure in my panel.