The author hasn’t clarified yet, but I suspect what they’re referring to is the fact that CORS does not support granular access control. If you make something public under CORS, any client can retrieve the resource if no other authorization or authentication check is in place. It’s not a system of authentication, it’s a system of authorization - specifically, for authorizing hosts to request resources which normally wouldn’t be authorized to do so under same origin policy.

As a concrete example: people occasionally misuse the Origin header, thinking that they can use it as a form of client authentication. The idea is that any client request from a non-whitelisted origin will fail. But any user can spoof their own Origin header, and the Origin header is primarily intended to protect users from making CORS requests they didn’t intend (because in most cases an attacker cannot coerce a browser to forge a header).