I suppose the first thing to say is that it is always nice to be given an explanation. I don't think anyone would have problem with "defective seat" as an explanation. What is harder to deal with for some is "operational reasons" because that could of course mean all sorts of things, including "someone more important has turned up unexpectedly and you are being bumped"- which makes it delicate from a customer services perspective.

Personally I would not get too fussed about it unless it (1) happened frequently and/or (2) caused serious inconvenience.

However I fear that you will not get very far with customer services. I had something similar happen to me recently, albeit in Y. Instead of row 6/7 window I was moved to 4 or 5 rows back (not exit) in the aisle. Not the end of the world, granted, but I like window seats. I asked BA for an explanation (not compensation- in my view it is clearly not worthy of compensation) but all I got back was "sorry you were unhappy but we cannot guarantee seats" or words to that effect. As it happens I was not particularly unhappy and I understand that they cannot guarantee a seat, but actually transparency goes a long way, and if they had given an explanation it would have been appreciated, especially if it was something as straightforward as "the curtain was moved", which may well have bee the case.

But it almost seems as though BA customer services is geared towards being defensive, almost like lawyers, and will therefore give bland answers for fear of making concessions which could lead to other liabilities. I think this is the wrong approach to customer services, but the overarching point for the OP is do not get your hopes up if you do decide to contact BA.