Is there any info how this was done?

The author commented on their ko-fi: "there isn't much to say that would require a big writeup - a lot of the code is already reversed, and anything that's missing can be yoinked from ghidra decomp output and cleaned up, so it's just a matter of transpiling to a different language. plus much of the game's proprietary formats are thoroughly documented by the modding community. time consuming but quite easy if you're just patient haha"