What does Category's attribute is_anchor do?

Question

I'm doing some sample tests from Magento 2 certification. There's this question (screenshot) I don't understand.

The correct answer for this question is A "This is the default category for a website", but according to my knowledge (I have been working with Magento for many years), if we turn Anchor on for a category, it's just enable the layered navigation for this category.

I wonder why the correct answer is"This is the default category for a website" when is_anchor is set to 1? can someone please explain?

Answer 1

That looks like an issue with the test question to me.

I would have thought the correct answer should be option 2:

The customer will see all products from all the children of the category

If is_anchor = yes, all the products for the current category and all children categories display, along with the layered navigation if filterable attributes are setup allowing you to filter the products.