How does Amazon 'Sold by Amazon'? Where did they get my inventory?

Did you ever have an FBA shipment that got lost in the past that you were reimbursed for by Amazon? If so and Amazon later found the shipment after reimbursing you then they will list the products to clear out of their warehouse since they have already paid you for the items. That happens a lot and is part of their terms. so if any shipments of yours ever went missing in the past that would explain it most likely.