Also not sure why this would happen, none of these products are linked to other categories?
Category A (master category)
SubCategory B (linked category)
Product in both would show in New Products box as "New Products for July - Category A) if you were viewing the SubCategory B page.
Always best to try and understand why something is not working as expected, however you can remove the '- Home Decor' part. It's near the bottom (line 85) of /includes/modules/new_products.php
Code:
$title = '<h2 class="centerBoxHeading">' . sprintf(TABLE_HEADING_NEW_PRODUCTS, strftime('%B')) . ($category_title != '' ? ' - ' . $category_title : '' ) . '</h2>';
Highlighted what I think is the relevant part -- if you make any changes, be sure to have a safe backup and use the template override folder!