The theory proposed is one I have never heard. I wonder if anyone here can confirm or deny it?
There were RAF men attached to the RNZAF in NZ in WWII, mainly those who came here before the war on attachment to help the RNZAF transition from biplanes to Vickers Wellingtons. When war began and the Wellingtons were left in the UK, they stayed on here and became very valuable instructors and squadron men, who's experience really helped to get the RNZAF going as it expanded so rapidly. But I don't know if they wore these shoulder titles.