Router device tracker shows "Home" when Away, on external network

My niece went to school, but her router device tracker shows her as Home. I set her phone up with the external network ( so she could access home assistant remotely.

But the device tracker from the companion app on her phone correctly shows her as away, and correctly shows her school address.
She has 2 phones. Her second phone with no companion app installed on it (thus no external network, and no connection to the router, correctly shows her as away.

Is this a bug? She’s not connected to the home router… Shouldn’t it detect / show her as away? How does the external ssl network connection work?
I wonder if it acts as a vpn which then tricks home assistant server to think she’s connected to the local network?
This would imply that the (Netgear) router integration is NOT showing connection to router, it is showing connection to home assistant server/software…

This nullifies the use of router device tracker in correctly tracking presence… Unless the phone is disconnected from the companion app…