Hi,
The issue is with the way your related products module is configured.
The "synchronize" setting is deactivated. Because of that, your module is discarding the "relation" setting and is displaying the products in the "main category" selected.
The "Relation" setting is set to "in the same categories" instead of "related products". And thus, even with synchronize setting activated, you would still not see related products but products in the same categories of the current product.
Also, the "sub element filter" is set to "direct sub elements" instead of "all sub elements" and thus you're seeing only the products directly linked to the main category.