Originally Posted by intuition

AY5413 is a codeshare. This means Finnair put their flightnumber on someone elses plane. In this case BA213. You may want to read up on the differences between marketed and operated flight.

Finnair does not have any Boeings and does not fly LON-BOS. BA does, and finnair sells ticket on that flight. What you have is a ticket sold by Finnair, but BA is the party that will fly you there.