It was booked through a travel agency, Opodo, albeit an online one rather than a bricks and mortar one.
I appreciate that the error came from the customer's side, but the agency have a duty of care to the customer and they have various robotics in place to perform quality control checks to inhibit processing of a booking where there is an error. Whilst it is theoretically perfectly feasible to have two passengers with the same name travelling together, it is a somewhat unlikely scenario, and one which in a correctly run and supervised system should trigger an alert and inhibit further processing until the customer has been contacted.
I know from two personal experiences with Opodo that they do not fulfil their duty of care to clients at all times. In this case, the client has received no extra value by booking through them, in fact the opposite has been the case.
I sincerely hope this customer succeeds in winning this case against Opodo.