I suspect that this is what has happened: BA has been publishing firmer plans for the northern summer 2022 season (starting on 27 March), and there have been quite a number of equipment changes. (As usual during "schedule change season", FT has exploded with "My aircraft has changed!" posts/complaints.)

Such changes take time to propagate through to codeshares, which often display out-of-date information for a while after the prime flight's listing has been changed. What you see would be consistent with IB's published information not yet having caught up. FWIW, I also see an American Airlines flight number (AA6969) and a Finnair flight number (AY5418) on the same flight, and both of those are still showing an A350 for that flight. I expect that all of these will catch up in due course. (So will Google, which is probably also out-of-date for the same reason.)

If you go to ExpertFlyer and look at the seat map for each of these flights, you will see that they all pull up the same 777 seat map, with the same occupied seats, if you need confirmation that you are looking at the same physical aircraft in each case.