One definition of "backed by" is "guaranteed exchangeable for."
Another is "supported by." As in 'Bitcoin is supported by the scarcity of energy available from natural resources.'
These are totally different definitions and the second one is made up. If you want to point out prerequisites to deal with Bitcoins, you don't need to redefine words. Bitcoins need the same modern capital structure that you also need for having dollars and modern banking. Namely, connectivity, electricity, equipment and many people employed in that area.
Back to the first definition (which is what most people use): what exactly and by whom is guaranteed to be exchanged for irrevocably spent electricity in case of Bitcoin?
The first definition only (strictly/literally) applies to currencies legislatively or constitutionally tied to a commodity, IE dollars on a gold standard.
The second definition subsumes the first, is more general, and more useful because it is more commonly used.
The second definition is not "made up." You are merely confusing your own lack of education with objective reality.
If you Google "backed by" you will plainly see every single dictionary listing numerous variants of the second defintion, as well as linguistic context demonstrating a preponderance of evidence testifying to the correctness of that usage.
http://lmgtfy.com/?q=backed+byWRT Bitcoin (and gold), a metaphorical blending of both definitions occurs, allowing Bitcoin's utility to be conceptualized as its backing.