This page explains in detail the interactions between the Game & Watch Gallery series and the Zelda series.
Game & Watch Gallery Advance
October 25, 2002

Zelda in the Museum.
The Game & Watch Zelda is available in the game's Museum after obtaining 60 stars at games, and becomes playable after earning 160 stars. Zelda is the last game to be unlocked, and it was probably meant as a surprise of sorts.
The gameplay remains loyal to the original game, but like all other Game & Watch Multi Screen games, the two screens are squeezed into one.
License
Copyrights for both series are held by Nintendo.