Interesting.. Which VPN are u using? If you don't mind telling! I am using Mullvad.
I am not saying app is smart. There is an app called "Where is my train" in my country, which works on the same principle i mentioned earlier. https://play.google.com/store/apps/details?id=com.whereismytrain.android No need to have internet access or gps enabled. Just need to be on the train and based on your signal strength to the tower you are connected, it will determine location of the train.
I am not running split tunneling. Split tunnel isn't going to work as i have enabled "block connection without vpn". In order for split tunneling to wo, this setting need to be turned off.
Edit: It is possible that, as i am running a regular android, some traffic are getting bypassed, which has proven in past that android leaks traffic when vpn is connected https://www.bleepingcomputer.com/news/google/android-leaks-some-traffic-even-when-always-on-vpn-is-enabled/