For those who haven't memorized the BA schedule, this is BA's LGW-BDA service, thus a Type 3 flight. All that matters is arrival at final ticketed destination. How late the flight departs is wholly irrelevant.

Having the destination information is useful because it is entirely possible that the time from wheels down to cabin open for deplaning was less than 5 minutes because BA was likely the only arrival at that time and there are no jetways to maneuver, so it is a matter of the ground crew simply pushing the air stairs the last few feet to the aircraft while the cabin door is opened.

It is remarkable, if indeed the arrival was at +3:59 that staff paid out EUR 600 because the sole reason that carriers track the "cabin door open" metric is for EC 261/2004. For the rest of the world and all commercial aviation purposes, it is "brakes locked."

I would send a note to BA, noting that it had paid out EUR on 600 on the other individual's ticket (providing both the PNR and e-ticket number) and asking that BA pay the proper amount. Don't get into legal lectures because they are lost on low level staff.

The MCOL process, if it becomes necessary, will reveal the correct answer because it is fundamental to the solution.