What model of fridge?! How did you know the random device on your network was your non-smart fridge? This is a wild story. I want to believe but if it's true I think there's no sane solution other than exploratory surgery on every appliance you buy.
So I went digging in UniFi, found it, and blocked it. Same with my HP Printer that sent almost a gig of data to Google Print Services daily.
> went digging in UniFi, found it, and blocked it
> still connected to my WiFi
Is your wife's phone also Samsung? Do Samsung phones have a habit of sharing WiFi passwords amongst themselves, or other devices with a Samsung Account? Do Samsung Accounts still exist? Is your fridge blocked, or is it still connected? If you change your WiFi SSID or password, does the fridge acquire it anew, the same way?