Unconsciously Incompetent.
You don't know what you don't know and would have no idea to search for info.
If they were patriotic enough to fly a flag I would reasonably assume they had no I'll intentions.
If they knew better they would have shoved it down where it couldn't be seen.
Approaching with flag in hand and asking if you can have it to properly dispose of it according to the flag code would be the better approach IMHO.....