I very much doubt it has anything to do with his size and more likely to do with his medical condition particularly as he flew over on a British Airways flight.

Obviously anyone that has had an operation or who has an ongoing medical condition has to be cleared to fly by a Doctor for their own safety.

The fact that this person is now taking a train and boat home indicates that other airlines are also not happy for him to fly and the reason would be that it is most likely dangerous for him to do so.