In the latter, do you mean thermal radiation or thermal conduction? I guess it doesn't make a huge difference because radiation hits you before you cam do anything about it, and conduction is impossible to get away from. But curious anyway.

Yeah those videos make me wonder. But my understanding from https://en.wikipedia.org/wiki/Effects_of_nuclear_explosions is that humans are quite a bit more resilient than structures. So a shock wave that utterly destroys an otherwise strong structure may not kill a human. However that seems related purely to the atmospheric shock wave itself. I guess shrapnel (even dirt), building collapse, maybe even "throwing the person" (so the ground, rather than atmospheric effects, kills) would greatly add to the indirect ways of dying. But is it most likely thermal radiation that actually does you in?