I can easily see the events of this dive happening. It's all too easy to forget to discuss buddy separation protocols before getting in the water -- this happened to me a couple of months ago, with someone I would just have assumed would follow the protocol I was taught, but he didn't. In addition, it sounds as though the separation occurred after a prairie dog pop to check boat position -- many people would assume at this point that the "dive" was over, and if they got separated, since everybody was headed back for the boat anyway, they'd just go. It's not how I do things, but it's not uncommon and probably not entirely indefensible. As somebody else stated above, I'd rather dive with Matt than with his buddy, but the big problem here was that they weren't on the same page.
Once Matt surfaced with a lost buddy, though, communication went south, and again, I don't entirely blame him. We are not taught how to communicate "I'm fine, but my buddy is missing" in signals to a boat. In Matt's mind, he was NOT fine, because his buddy was missing, but in the captain's mind, he needed to know if the diver he was looking at required assistance, which Matt actually did not. Seeing a low mileage diver in a situation like this, I'm not surprised that an effective sequence of signals didn't immediately occur to him. Learning to improvise signals is something I think most of take some time and some odd experiences to do.
Once everyone was back on the boat, though, things could have been repaired fairly easily. I think an earnest explanation to the captain of WHY Matt chose not to use the OK signal would have been received well -- perhaps countered with the reasons why the captain thought he SHOULD have used it, but all in all, an amicable exchange. But if I were the captain, and asked, "Do you know what this signal means?", and someone just stared at me, I'd get increasingly irritated, and things would probably go much as described.
Somebody already brought up the adrenaline hangover that parents feel when they find a lost child and scream at him. I think some of that was operating both for the captain, and for Matt. Being anxious and confused about losing a buddy you feel responsible for, and being confused about how to communicate that over a distance where voice wasn't useful, would leave me anxious and frustrated -- and I would have been more than a little annoyed, myself, to find my "lost buddy" relaxing on the boat. At that point, you can do one of two things. You can simmer in your righteous indignation, and skip the second dive, and irritate everybody on the boat, or you can take a deep breath, chalk things up to experience, explain yourself pleasantly, accept the buddy's apology, and sit down to do some communication and some planning to prevent the same thing from happening a second time. You can stay stuck in the moment, or you can look forward and get past it.
I have a very good friend with an awful temper. When he loses it, he makes everyone around him uncomfortable and unhappy. He knows that. After one of his eruptions, he ends up pretty much alone, because nobody wants to deal with any of the awkward emotions that go along with such an episode. People who cope gracefully are much more pleasant to be around than those who are sullen or can't let go of things. Life is full of great experiences and good stories -- if you aren't having the former, you should be planning the latter