Steam keeps counting "time played" while your PC is in Sleep mode with a game still open. Factorio is quite small, resource-wise, so keeping it open in the background is convenient.
Not saying this is the only possible explanation for 7000 hours. It's just something I noticed when my "time played" was way higher than what is plausible.
Not saying this is the only possible explanation for 7000 hours. It's just something I noticed when my "time played" was way higher than what is plausible.