I suppose perceived size is subject to ones' prior experience (I know, "thank you Capt. Obvious," right?). I thought one of the reports said the boat "backed into the buoy?" That was why I didn't settle on the scenario you laid out. If it was bow-first, then yes, the first two getting pushed away by the hull makes sense. If stern-in, I suppose if someone on board had hooked the buoy and had a good capture, if the boat continued to reverse back over the mooring--and if there was a lot of "play" in the mooring, the first two divers might have been held close to the swim step while the second two (now holding onto a relatively "slack" line) would have ended up, well, where they did.
If the Captain was as bad as the thread implies, I suppose it's possible for all the above to have happened so fast that either A) the divers were REALLY focused on something else and didn't realize the danger that was approaching or B) the divers did realize danger, but chose to (instinctively or otherwise) cling to the line for safety.
Question for the thread...back when I was able to observe divers on a daily basis was the era before smartphones. Computers were common, but people tended to glance at them when needed, then go back to looking elsewhere (buddy, up, down, around, reef, stuff growing on the line, fish swimming by, etc.). We're now living in a world where a large percentage of humans can't seem to look away from their screens for more than a few moments at a time. Do you all see people just staring at their computer all the time these days? During a safety stop or whenever? That seems like a dumb question, but then.....well, people, right?