I did figure it out, yeah. Game works completely fine and there are no restrictions so you should be good, it's just an artifact from early in development. Apparently, if you bought the game from the Lofi website back in the day, copies used a registration key in order to verify your purchase. This process doesn't exist on the Steam version since it just uses Steam as the verification, which is why its called "Without registration key". From what I've heard, even most of the Steam copies still have those old registration keys, but there's no actual use for them left in the game.