My first impression was that they were on staff travel (not necessarily actual BA staff). The circumstances seem a bit odd though.
Reminds me of when my little brother flew back from SYD and was assigned a boarding pass with seat Jxx indicating a jump seat assignment, he was lucky enough to be given the crew rest after the flight deck had finished with it. Now there's some jealously to having a boarding pass with J before any seat number but not sure it' worth it for the pain and suffering!