The Match score is calculated based on the product keyword search term you use and it is matched against the commodities imported by the suppliers.
You will find it right under the Supplier's name and only shows when doing a search by Product:
We match the products keyword with their HS Code description along with the product description laid out in the Bill of Lading to ensure accuracy. The supplier’s match score will increase based on how well the search term matches to the HS Code and Bill of Lading.
Suppliers will get a higher score if their top products exported match the search term.