It's not uncommon for software to claim to offer this feature. Windows does it for example, and it was a bug in such a feature for WebCrypto in Firefox that made the news recently here.
Invariably such features are weak and a sufficiently capable attacker can override them. In Windows for example you could reach into the opaque data structure and toggle the Boolean that forbids exporting keys...
Maybe the concept is the same, but on a Mac the private key is stored in the Keychain instead of a physical enclave?