More like: we all need arginine, but our body makes it, so we don't need to supplement it. Wikipedia writes this:

Preterm infants are unable to synthesize arginine internally, making the amino acid nutritionally essential for them. Most healthy people do not need to supplement with arginine because it is a component of all protein-containing foods and can be synthesized in the body from glutamine via citrulline.

I have no idea if he is right about what he claimed, but can small really stand in for prematurely born or carrying relevant rare genetic mutation?