“It’s the IP address of the device”
“Anyway if you see the same IP address at multiple locations”
IP address for a phone is not fixed but depends on which data provider you are connected to.
For example my phone’s IP address is currently the same as my laptops IP address because they are both connected to our home wifi.
But if I switch off wifi on the phone or travel outside, the IP address will change and will depend on what cell phone tower it is connected to.
I could be mistaken but the phone and laptop should have separate IP addresses. It would think it would be an IP conflict if the two are connected on the same router.
I agree it can change, and can change based on the router or 5G tower. Maybe they meant the IMEI device ID or some other way. In any case I have no doubt it is possible to scan and check devices, law enforcement does this all the time.