Hi,
The 'HikaShop Shipping manual - Prices per product plugin' appears on the list in J2commerce for Shipping plugins. It happens with the default installations of Hika and J2 on the same Joomla instance.
In the Joomla core Plugins list the Hika plugin has a Type of 'Hikashop' and an Element of 'shippingmanual_prices'.
I suspect it is the Hika plugin's element name that is similar to the J2 element names that is causing it to get picked up by your filtering.
Regards,
Terry