This is not reverse engineering by any definition of the word. Even in my country, where looking at the copyrighted code is legal when it is done for "interoper

This is not reverse engineering by any definition of the word. Even in my country, where looking at the copyrighted code is legal when it is done for "interoperability" purposes, you just CAN'T decompile the thing, ship it and call it a day. My implementation being remotely similar to the original one would get me into trouble. Here, they are distributing literally a clone of the original game, down to the same checksum. Not only it is a useless legal defense, it is absolutely idiotic to think that it would be. And in many countries of the world (including the US), not even looking at the copyrighted code is necessarily allowed. See the entire clean room thing.