Nothing in terms of health is a one size fits all. I wouldn’t take that comment to be a prescription for literally everyone.
A strong argument can be made that if you had to mandate one diet for every single human, a 100% animal product diet would result in the least sickness/illness in the population.
I think human resiliency in terms on what foods individual people can tolerate is sometimes confused with thinking those foods are net beneficial or good.
When you break down what the body needs (essential amino acids, fatty acids, minerals, and vitamins) you will be hard pressed to find a better source for those nutrients than animal products. That some people can eat plant foods for entertainment or social bonding purposes is perk imo