(MY THEORY BTW) This was planned, but ultimately nothing was made.
From The Lost Media Wiki
Think about it. It was mentioned in the source code AND a frame for a Gameboy camera, and yet nothing else was ever made for it. If there were more pictures (for example, the super Mario world arcade game that was not the roulette one) then it would have a higher chance of being real. This THEORY also applies to the Pokémon sun and moon prototype (something and stars).