If you bring up the details for that device, there's a link that says "How location and times are determined" -- this is what it says:
"How locations and times are determined
The locations shown are estimated from the IP address assigned to the device by the Internet service provider. Estimations based on IP address can be inaccurate, so you might see a nearby city instead of your actual location. Saving the IP address also helps Google identify unusual sign-ins and protect your account.
The times listed represent the last time there was communication between the device or session and Google’s systems, at each location. This communication includes both user actions and automatic syncing."
What kinds of activities have you been doing the last couple of days? Have you been specifically using Google services, or primarily using some non-Google app?