It shows phones like galaxy s5 droid 4 and note 3 on my device manager I never even owned any of those phones I change my Google password every other month. I don't know why its showing those devices.
are you sure you havent logged in on some devices of those? I remember i used my google account on a friend tablet and later when google added the feature to sync devices i was getting synced with the tablet. Took me months to realize where all these photos come from