Apart from all the other comments here - UniFi's network monitor being garbage, the app using the Facebook SDK for login, etc - the real reason your thermostat

Apart from all the other comments here - UniFi's network monitor being garbage, the app using the Facebook SDK for login, etc - the real reason your thermostat or fridge or cat feeder or vacuum cleaner sends data to an adversarial network is because it can. When you bought the device and skipped over the small print to get it to do what you bought it for without having to plough through half a bible's worth of legalese you, most likely unintentionally and unknowingly, gave it permission to do stuff like that. It would have been worded in woolly phrases about 'sharing data with partners' for the purpose of 'improving and personalising service' and possibly to 'present targeted offers from partners' but all that is just newspeak for milking your data for profiling and advertising purposes. The solution is equally clear and simple: don't allow these things to access the 'net, put them behind a firewall which only allows traffic inside your own 'controller area network'. Use a VPN to tunnel into this CAN to set your temperature, feed the cat, mow the lawn and whatnot. If this sounds elaborate you might want to consider doing away with all this 'smart' functionality and just get a 'dumb' fridge/vacuum/cat/etc.