And without knowing an appropriate signal, how exactly do you communicate this from 200 yards away? His options at that point are pretty black and white... either everything is ok or something is wrong, and he felt as though he needed assistance.
If a search was needed, it may have been delayed... but they then might also have had a head start on where to begin looking, since he's still in the general area.
I'm trying to visualize this event and put myself in the shoes of both Matt and the captain so I can learn from this. For instance, what if you happen to come across a diver who is so entangled in line that he can't be freed and no one has a cutting device (or add any detail you see fit to make the point that you need extra help from the surface for an emergency that must be handled underwater in a timely fashion). If I surfaced to get help from the boat and found that it was far away, I'd be waving my arms in distress like a madman. If I were the captain, I'd get the boat closer to the diver before sending someone in to rescue the person on the surface. At that point, I would assume you can communicate the real issue at hand and appropriately handle the situation. Am I wrong for thinking this?
After reading this thread, if I were in the above situation, I think I would give a variety of rotating signals - starting with waving my arms around (to get their attention... and like Matt said, to HOLD their attention), then the big OK sign, then the pick me up "field goal" sign... and I would repeat this sequence until they were close enough to where we can verbally communicate. Am I wrong for thinking this?
... and since I haven't commented on the aftermath of the incident, quite frankly because I'm only interested in the emergency issue at hand, I would like to add that Matt probably handled that better than me. I have the utmost respect for captains while on their boat. Paying customer or not, I will always immediately do what they say, no questions asked. However, if I was belittled by a captain in the manner Matt describes, I would have punched him right in the face, no questions asked.