Does this have the Nintendo logo in the ROM header? Real GameBoys check the ROM for an image containing Nintendo's logo during boot up as a way to prevent unlicensed games. The idea is, to make a GMB/GBC boot, you must at least commit trademark infringement, which gives Nintendo more legal leverage to block/punish any attempts to sell anything that Nintendo didn't get a cut of.

If the logo is missing, it would still boot on an emulator that doesn't emulate the boot ROM (which is most of them) and probably most flashcarts, so there's no need for it to be in their release. But it's still possible that whatever build system they used automatically inserted the logo.

There's no way Nintendo would bother McDonalds legally over something like this if the logo's in there, but I'm still curious if it is.