This is why i dont like these kind of studies. Clearly it does not take 60 hours to find a dead tree in the woods, break it down, and light it on fire.
The original study estimated 10 pounds (5kg) of wood foraged, trimmed and dried per hour of labour. That sounds low with a saw and an axe (and very low with a chainsaw), but might be about right with primitive tools including travel and processing and wood stack maintenance (no tarps either).