Probably left it running? I've definitely left my factory to idle to build up resources while I'm gone, when I'm playing on peaceful mode. You could also run h

Probably left it running? I've definitely left my factory to idle to build up resources while I'm gone, when I'm playing on peaceful mode. You could also run headless version of the game on a server and just connect to it for the same effect. Remember - Factorio is just an idle game with extra steps.