The fulfillment status of each item in the Product Tracker reflects which type of seller is currently the Buy Box winner under the given ASIN. Take ASIN: B076SVC7SN for example. The fulfillment type is shown as FBA.
On the Amazon selling page, there are two sellers under the same ASIN.
According to the offer listing page, the current Box Buy winner is FBA. Given this, BigTracker displays the FBA status for this ASIN.