Don't know the guy or his vids, so will just comment on practicality.

Other than very mild (no colder than 60s overnight) hammocking absolutely requires insulation below, on the sides and above. An emergency bivy has no insulation whatsoever; it's a simple shell. I can't imagine this as my sleeping system anywhere other than the tropics.

Secondly, wriggling into a bivy when inside a hammock (limiting myself to an enclosed Hennessy-style hammock here) is darn near impossible. You basically have to be inside the bivy while still on the ground, then wriggle up and in while wearing the thing. Same goes for a mummy bag without a full zip. I file this action under "N" for No fun whatsoever.

FWIW I kinda like hammocking in the rain provided I have a riggable fly that can go far enough overhead and covers enough area to hang out under. It can be nicer than hunkering inside a smallish mountain tent and gives me a sheltered spot for cooking.

Cheers,