The guy should be more precise. He said Pando is the largest. But he also said the fungus consumes more land area than Pando.
So though it may be more massive, it isn’t the largest. Also, nobody said anything
AFAIK about the weight of the respective organisms.
I could see the fungus, at over 2,000 acres and mostly made of water, possibly being heavier than Pando.
Thing is, there’s not much drama in sleeping on the ground because an enormous fungus is amungus that you can’t even see.