This really shouldn't be necessary. While I don't use MacOS myself so cannot verify, under Linux, I can take any Windows RPGM game and literally extract the nwjs release into the game directory (overwriting any files that clash) and execute the 'nw' binary left in the base directory either by double clicking on it or with ./nw in a terminal in the directory. The game then runs natively as if I had run the exe for Windows, on Windows.
Perhaps MacOS really is different, but I doubt you need to spin up a web server, I think this guide is probably ...misguided.
FYI, my method for running any RPGM game under Linux is always the following.
Download the Windows release for the game, as well as having a somewhat recent copy of nwjs for Linux saved somewhere already, then,
Code:
7z x Game_WIN.zip
cd Game_WIN
tar xvf ~/Downloads/nwjs-sdk-*-linux-x64.tar.gz --strip-components=1
./nw
And it just runs.
The only issue I ever experience is case insensitivity incompatibility (some developers will reference image.png as Image.PNG and it will error), but MacOS is a case insensitive OS if I remember right, so you would never experience this.