Ryanair does have Priority Boarding on all flights. It's charged for (I believe 5 Euro each), but if it's an important issue for you, why was this not paid ?
Quite possibly the passenger in the A seat had already paid for this facility themselves. Quite why they should then, at a late stage in boarding, have to give it up for the sake of those who couldn't be bothered to pay the priority boarding fee eludes me.