Nothing from the opening post or elsewhere justifies accusing OP of some devious attempt to 'upgrade' her husband by seizing the precious UD seat next to her own, and I suspect if OP had been on the lower deck it would have been a passenger from there who would have been asked to go upstairs.

The problem is OP's apparent feeling that BA should have done more to accommodate her wishes, because aside from expecting BA's systems to have some psychic ability to tell when passengers on separate PNRs are actually travelling together, the only thing 'more' that BA could have done would have been to re-seat someone else without their consent. Such a practice would represent a very unfair privileging of couples over solo passengers.