In theory yes, in practice ... if that's true, why would anyone ever hire you for your experience? You wouldn't be allowed to use it.
But isn't that exactly why you as an interviewer would pose a problem, set up the context that is potentially similar to the work your project would require, and see how the interviewee navigates that?
And I sure would hope they bring all their experience to bear! Just because they learned about CDNs at their previous job and “everything is proprietary”, I don’t want them to suddenly forget how CDNs work.
Very little is actually unique between software businesses. We’re mostly just doing data bureaucracy.