I may know this person, or someone reasonably similar.
About 10 years ago, I was involved in a very unusual instructional situation. I was assisting in a class of 5 students, including a teenage brother and sister. We learned after the class began that both were autistic. The autism spectrum is quite broad, and many excellent divers are on it at the high functioning end. These two, however, were a serious challenge. I later learned that the brother was so severe that he required a full time personal aide in school, and that was often not enough. We quickly separated them out from the rest of the class to give them greater attention and allow the other three students to get through the materials. After many, many sessions and infinite patience on the part of the instructor I was assisting, the sister eventually got fully certified.
The brother was more of a challenge. He was very big and clumsy, and he had other characteristics similar to what was described in this incident. The instructor finally convinced the mother that he could never be an independent diver, so he finished with a scuba diver certification, which required him to dive with a professional on all dives. The hardest part of that was convincing the mother.
What strikes me in bringing this up is the statement that "The diver did not make special arrangements with the dive crew...," yet he dived with a DM. It sounds like he showed up with a scuba diver certification card and no other explanation. This is extremely consistent with our experience. The mother gave us no warning whatsoever that her children might need any special help, even though the son required a full time aide in school. She was adamant in her belief that her children should go out into the world as any other person would. She refused to give us any warning that they needed special help (and they really, really did), and I am sure that she passed that attitude on to them.
As a career educator, I worked with special needs students to some degree all my life, and the attitude I described occurs commonly among parents. In many ways it is admirable. In many ways the child is consequently able to do more than people would think possible. In many other ways, though, the child could benefit from learning to admit that a little help is needed.