I might be reading a different version of the article than you did, but the article agrees with you - URIs are a superset of URNs and URLs. I didn't see where t

I might be reading a different version of the article than you did, but the article agrees with you - URIs are a superset of URNs and URLs. I didn't see where the author says there are no URIs which are URNs - the article specifically says 'a URN is a type of URI with the scheme "urn"'