The "Buy Box + Shipping" column is not a new feature and we used to just display the Buy Box price that we receive from the repricing SQS feeds from SP-API. The system displays the Green check mark when your price matches the Buy Box Price.
This is similar to the concept of the "Lowest Price + shipping" column. Now the filter "Listings match buy box price" will actually show you all listings that are at the same price as the Buy Box offer.
The listings that are displayed under this Filter are not necessarily in the Buy Box, but there is a good chance that they would be in the rotation for the Buy Box ownership.