Here is an example of someone who cares about the behavior and/or the documentation (and still cares enough to check up on their StackOverflow question six years later): https://stackoverflow.com/questions/13833566/python-argparse-choices-from-an-infinite-set/13833736 .

The issue is not the use of the word "container".  The docs literally say "Any object that supports the `in` operator can be passed as the choices value" and that is not true.  In fact, changing it to say "any container type" would be an improvement as that is at least arguably correct, whereas the current documentation is unambiguously incorrect.