You must be wondering how to use the Reset variants quantity to 0 if unmatched with SKU or Barcode in the feed file.

Did you know your Filtering Shopify Products affect this option? Actually, it makes the option much more precise and you won't go resetting everything to 0.

For example: 
You will notice it will only reset all variant quantity to 0 if it unmatched against all variants under vendors Adibas.

Basically, you need to add to include the vendor Adibas in the Filtering Shopify Products.