any trigger that has a distinct “user interaction” of any kind (like tapping an NFC sticker, or getting into a car, or opening an app) can execute in the background.
triggers that might occur without the user noticing can not run without a confirmation.
one could of course argue that arriving or leaving a place is a physical action the user is aware of - but even like this the story checks out in my mind.
also, I am pretty sure that it is not about battery, but about Apple being Apple.
they will not allow you to accidentally do funky things you are not aware of - even if you really want to. like it or not: sounds 100% on purpose to me