It's hypothesized that soaps originally formed accidentally when basic rain runoff from expired camp fires chemically interacted with animal fats. Roman sources certainly document the production of soap from tallow and ash, which is a circumstance that could conceivably arise by chance in aftermath of a camp fire. Perhaps that's not natural, or maybe we can theorize some sort of wildfire scenario causing the same circumstance.

Regardless, I think his point is that shampoo as we know it today is very much a product of the modern marketing/industrial complex.

In small quantities, sure.