What is the "Debugger's Gift" Rhydon in Red, Green, and Blue?

Question

The Bulbapedia article about underleveled Pokemon has a section on unobtainable Pokemon, the first of which is a Level 5 Rhydon in the Japanese Gen I games. The location, "Debugger's Gift", is not explained in the page's discussion section or history, so I'm pretty stumped on what's being communicated here.

Any context would be appreciated. Thanks in advance.

Comments

no idea but if I had to guess since rhydon was the first Pokémon that gamefreak made the devs in a gamefreak building were supposed to give it to you. However I really have no idea I was just theorizing