draft-ietf-websec-key-pinning-21 - Public Key Pinning Extension for HTTP Section 2.5 "Noting Pins" requires the server to set a backup pin:
The given set of Pins contains at least one Pin that does NOT
refer to an SPKI in the certificate chain. (That is, the host
must set a Backup Pin; see Section 4.3.)
An example is Qualys SSL Labs - Projects / SSL Server Test / sw-servers.net, which only sets one pin. I think it's better to give it a warning, rather than a green "Yes".