I cannot translate in German from mobile, I'm sorry for this but yes this is how it works on any EV or plugin cars.
The battery is only charged when you are driving and when is needed by a DC/DC converter.
I see no technical reason for this, the dc/dc does not need any movement to work.
It is a real mistery for me why SOME electric cars use this approach while other have a "battery saver" which periodically turns on the dcdc to charge the battery.