I presume that he means that he would issue a note (if you were unable to travel) that it is now inadvisable to travel. Some airlines have reduced/ waived cancellation fees under such circumstances.

Of course, it is a grey area: insurance companies would be pretty unhappy with a doctor who basically says that they would issue a medical note for the sake of convenience (not completely implying that's what he's doing -- don't know enough to say).

tb