I was just in my Google about to make sure my photo privacy settings were set correctly. Under security it showed that 3 devices were linked to my Google account under "signed in devices". One is my mobile and one is my laptop. The other is a mobile phone model that I don't recognise but is possibly my ex husbands. We have a shared Google family account to manage DCs online activity. I assume that's why it showed up. Would that make sense. Although my childs phone doesn't show.