One has to assume, there was a BIG FAT RECRUITING COMPANY MOGAL who trawled all the relevant Officers Messes for those leaving. You only need one to sign up, and it would get round like wildfire.
Thats how it normally happens I suspect. It would never get into an RAF leavers journal or be that obvious, just something down the lines of a "Foreign Government Needs You" to teach them to fly scenario.