If we are envisioning a single “nuclear explosion” (not a large nuclear attack), then this advice is not as crazy as it might seem. Think terrorism, or accident. If you survive the initial event, and the rest of the country is immediately in a position to render aid, then your objective is just to stay healthy and safe for the 1-4 days it would take to start getting things sorted out. In that scenario, access to clean water, first aid, and not getting covid actually seem like reasonable things to worry about.
There’s not really any good advice in a MAD scenario. Only a tiny faction of people would be able to set out for the wilderness and survive. The vast majority will die of exposure of one kind or another regardless of how much prepping they do.
Well, also the wilderness can't support a large foraging population for more then a couple weeks at most. Like, there are straight up too many people for wilderness survival to work at scale - North Korea is in widespread ecological collapse because its population has essentially stripped the wilderness bare trying to survive.
There’s not really any good advice in a MAD scenario. Only a tiny faction of people would be able to set out for the wilderness and survive. The vast majority will die of exposure of one kind or another regardless of how much prepping they do.