Windrush was a troopship (Ex German we kept her as a "prize of war") she was returning from Austrailia with servicemen when she called into Jamaica.
A notice was put in a local newspaper offering a cheap trip to the UK
Presumably the RAF Movements officer was there initially to meet the returning servicemen and was greeted by a number of Jamaican ex-servicemen wanting to re-enlist.
Reading about the first lot to arrive it wasn't as organised as I certainty thought it was originally.
I was led to believe they came at the invite of the British Government but reports has the Government having debates as to whether they could land when they arrived
They had no where to put them and many were billited in old air raid shelters.