According to your quote, CK has some APIs that depend on the enclave, but SC does not support those APIs.
It says nothing about whether any other SC APIs use the enclave behind the scenes (but I doubt it, there's not much point in bothering with the enclave if the CPU has access to the key material).
I think the point he's trying to make is that the CK implementation of the APIs common to CK and SC may (or may not) make use of the secure enclave, and that's one reason to have different implementations.
It says nothing about whether any other SC APIs use the enclave behind the scenes (but I doubt it, there's not much point in bothering with the enclave if the CPU has access to the key material).