i think that is a misunderstanding
1. bitcoin is not backed by something and "proof of work" is just a mechanism to defend the network against attackers trying to rob everyone
2. money is never scarce. the wording is misleading - i agree. only goods and services can be scarce. a limited money supply does not make it scarce, it just standardizes is - is 1lg or 1m as a standard measurement unit scarce? ...would you want constant change in what 1m or 1kg means?