No, LB does not make playlists based off a folder name. Honestly, I think this is the first I have seen a user post trying to do it this way. Most (not saying all do this, just most seem to) users typically have roms for a platform all in one folder and then let the software create the playlist based on metadata.
Indeed they did. That is why you see LB can either create a bunch of predetermined child playlists for each system or the user can just manually create a playlist based on multiple requirements of choice. When you make a playlist just tick the box to make it an auto-populating playlist and set that parameters.
If you are not checking the box to "Auto-Populate" the palylist you made you just create the playlist then save it. You then go into each platform (or go into all games) and select one or as many games as you want then bulk add them to that playlist. It is not done from within the create new playlist window.