Hi,
So you maybe have a module displayed on that menu page, or your products have the main category as category too.
Please check in the product edition pages the linked categories, if the main category is present, so it is normal that the products are displayed.
Please check that you don't have an override on the view "product / listing", if it is please do a backup of the code, and remove the override, this can potentially cause the issue.
For the category image, this should maybe be in the product part indeed. We will think about that.