I believe that the claim is this: In the long scope of history, being able to accumulate money without having to be strong enough to defend it is really rare.

> that saving is somehow unnatural

Depends on how you define saving. Hoarding perishable goods is of course a pretty natural behaviour but that only scales so much. Investment (i.e. owning more land or other productive assets than you can utilize directly yourself) seems pretty as opposed to communal ownership seems pretty "unnatural".

Not that I'm somehow implying that "natural" (whatever that really means, since using violence and coercion certainly seems like natural human behaviour) is somehow always superior to the opposite.