> The guy's voice is almost a whisper, the ambient sounds from the garden or the forest or the road are oddly pleasant, and he's speaking pretty slowly, with none of these glitchy quick cuts you see in a lot of YT content. It's also unusually personal-feeling, like he's just talking to you.

This sounds very much like ASMR. I find the most relaxing/entrancing videos are the ones that are unintentional/not forced, although obviously personal preferences do vary.