G'day Hurrah,
I too like Decrepit am a windsurfer.
I have actually tried to rescue a kite which went on a solo run. My recommendation to any one else is to stall and park the nose of your board on the actual kite to stop it taking of again. hop in deflate the main bladder roll the wee beastie up and bung it between the sail and boom on the leeward side.
Sorry if it sounds a bit rough but on my rescue mission I got one of the lines caught on my harness hook and got taken for a 15m drag (away from my gear) before I could get myself unhooked. Serious brown undies time.

I have managed to rescue a board though(the hard way)by trying to hold onto it and water start, it's bloody difficult. When I finally got to shore, the brain kicked in and I realised that I could have tied it to the end of my boom with my outhaul rope, would have made the rigg a bit heavy but it would have been a schidt load easier than trying to hold it. I believe the going rate for this is a Carton.
Realistically at the end of the day, it comes down to your own personal safety. If you think you can do it safely then it is the rescuers call. At the end of the day gear can be replaced.
As you were on the shore and your rig was floating away the other dude on the beach made his judgement call.
If it had been you in trouble and not your gear out there he may have offered assistance as should we all should do if we see some one in strife at sea.
Alby
It's all just a minor ripple in the cess pool of life!
Surfs up Baby!!