If still suspicious, maybe see in the settings if the supposed unknown device shows up differently or if your account has ever been accessed before?
( While signed in to your gmail, or at least browser version). Click on Avatar==> "manage your Google Account" ==> Security ==>(scroll down to) "Your Devices", ===> "Manage All Devices" and you can log out anything. The activity and time stamp, will show up for each one.
Not sure how helpful that will be, but that is the only other tool I can think of they have.