Personally I don't agree with your friend who used to be a professional and famous windsurfing coach.. btw.. Who is he?
I have found that most helmet wearers are just sookie la la's..

You know.. The type who always wear helmets on skateboards and roller skates..

.. Just kidding..

Then there are those who charge big waves and don't want to get hit on the head by their board.
Also those who have had a hit on the head and think that they were lucky to get away with it once and don't want to push their luck.
Dogman always used to wear a helmet before he became a legend..

I remember him saying it was for sun protection reasons. (or maybe that was someone else).
I don't have anything against helmet wearers.. and I don't think there is any need to stay clear of them..

DJ