The only thing I can think of is that "whomever you are talking about" has "something else" that is interacting with the car. Some third party app or other, that can also interact with setting the charging.
One other thing just came to mind, and thats the fact that the car will try to charge at whatever the last setting was, for the place you are at. If the last time they charged "wherever they were" was 100%, that might be saved as the default charge percentage for that location, till they change it to something else when they charge there.
Those two things are the only thing I can think of, but since its not your car, It could be difficult to find out if they ever at any point tried any third party app that can interact with charging, or if they set 100% as a charge rate at a location.