That's what Oauth is though. Oauth is NOT a single sign-on technology, it's about granting access to data across services. OpenID is a single sign-on protocol built on top of Oauth.
Note that there's older OpenID (without "Connect"), which, to my knowledge, is more or less dead nowadays, and OpenID Connect, which is indeed built on top of OAuth. Both are indeed SSO, though.
Splitting hairs but no, Oauth has nothing to do with authentication. An introductory article like this should address the distinction between authentication and authorization in the first section IMO.
Distinction which is totally useless in practice as you certainly won’t have authorization without authentication.
At that point, the separation is more about capabilities/responsibilities than "does it happen?"
(This is what I do in my day job.)