Thanks for the very nice comments everyone! The stem is drilled with a curved tool and the draft hole opened up through the bowl to finish it off. It does pass a pipe cleaner, however the cleaner comes out curved! These were made by Alain Albuisson for BC, I think it's from the 80's judging by the inlay. The only other company I know of that uses these curved tools is Ser Jacapo but I could be wrong.
@Toby, there is no extension.