[EMIRELADERO]

It is more likely to be fair use in this specific instance, as the copyrighted work to which the analysis is applied to is the whole game, not the code itself.

A big part of fair use analysis is in the effect on the market for the original work. If people have to obtain a copy to even use the project in any interactable way, the effect is either none (if we suppose every user of the project gets their original copy illegaly) or positive/benefitial to the copyright holder (if it makes those users actually buy legit copies)

[charcircuit]

The game is a copyrighted work, but so is the source code. The compiled code is a derivative work, and so is the decompiled code. Nintendo is not selling the source code, so arguing about sales in the market does not makes sense.

[EMIRELADERO]

The fair use analysis is done on the work as a whole, the Zelda game that's registered on the Copyright Office. Not the code only.