Just that Suyu isn't doing anything illegal or against the law. Emulation is legal. Also reverse engineering if it's done right in a lot of countries. What discord did here wasn't because of the law but because they are feared of Nintendo being mad at them.

Yes. Contrary to what some Americans think, the rest of the world isn't ruled by the US and their often ridiculous laws don't apply. For instance in this case, neither the code nor the community discussions have anything to do directly with Nintendo. In addition, emulators and reverse engineering are perfectly legal in many places. There are plenty of jurisdictions where such frivolous and preemptive copyright strikes won't even be tolerated.