I think it's a more exclusive qualification.
But I thought they looked top quality! The caption says it all.
IIRC, it's something as simple as capitalization, like Big Bird is a mupppet, but he's not a Muppet.
As for the story itself, if it wasn't obvious just looking at the 3 main muppets that the Jim Henson Company was involved, the assistant character had a big blue nose reminiscent of a member of the Dr. Teeth & the Electric Mayhem Muppet band.