It indeed was the sixth anniversary of the show. Little else is known about the show except that writer Paul Rhymer played a trick on the listening audience -- maybe even a trick on the cast -- by having an actor come in at the very end of the program to play Mr. Gumpox on the air. Gumpox' only words were, "Hello folks."
(We now know that in episode 33-06-14 Rush Gets Kissed by Mis' Wilcox, that Mis' Wilcox had several lines - long5 years before Mr. Gumpox.)
This was just a gag by Rhymer, certainly to celebrate the 6th anniversary of the show.
Cliff Soubier played the voice of Mr. Gumpox.