Peak Prosperity was not about prepping much at all until Covid, as far as I know. Dr. Martenson started pushing home gardening and stocking up when covid hit--in fact, he started saying such things in like February 2020--pretty prescient.
Edit to say: I don't think saying the virus came from nature requires any additional proof. The claim that requires extraordinary, indisputable proof is the claim that it was man-made. And I have yet to see it, from this or any source. Just a big compilation of weak, circumstantial evidence.