Yes, because not understanding something and not knowing something are two completely different matters. And not "what the story is about". They're ignorant of what the story is. I.e. they don't know the story proper, their complaints are just based on some random bits they snapped up.
For that matter, this lack has nothing to do with the story being to hard for them to understand (because it really isn't that complex) and a lot with them not bothering to even check what it is.