This shows up in the text for the auction:
"Was made in 1996 for Tangi Tully’s Birthday. It was the display mascot for Tangi Ukuleles. It was built just like a regular ukulele and to scale. What is remarkable is that it is playable and tunable. Thickness of wood is to scale."
It's a plausible explanation for why the ukulele was built. The asking price, however, may be a "joke."