Hi,
Go in the menu Display>Content menus and edit your menu item. There, you'll find two "sub elements filter" settings. The first one for the categories listing and the second one for the product listing.
These settings define if the listing should display all the elements directly linked to the current category (direct sub elements), or all the elements directly linked to the current category + their sub categories and the sub categories of their sub categories, etc (all sub elements).
So make sure that the "sub elements filter" setting of the products listing is set to "direct sub elements" and that will do what you want on your listing.