If you read Shadow Divers about the story of Chris and Chrissie Rouse, you might want to read The Last Dive, which goes into that fatality in much greater detail. it also goes into the difference between the cave and wreck diving--at least as it was then.
The two traditions evolved differently with different divers, and they used different approaches. The big difference then was the system for avoiding getting lost. Cave divers developed the system of always having a continuous guideline to the surface. Wreck divers used a system called "progressive penetration"--gradually go deeper and deeper into the wreck over a series of dives so that you get to know it. That difference has since faded away--most wreck diving courses teach the continuous guideline system now. I have not heard anyone preach progressive penetration in a long time.
Chris and Chrissie came from a cave diving tradition, and they ran line when they penetrated a wreck. In contrast, if you ever see the video John Chatterton made of himself diving that Uboat, you will see that he did not run line. Chrissie ran line into the wreck on the fatal dive, when the shelving fell in on him. His father had stayed outside the wreck because of the lack of room, and he was able to free him, but in doing so, he lost contact with the line, and they evidently were unable to find it again. They apparently got lost and came out the wrong hole.
What killed them, though, was narcosis.
Chris had had some financial setbacks, and he could not afford helium for the trip. They were diving air at about 230 feet. chrissie was narced out of his mind. He never knew that a shelving unit had fallen on him. He thought a sea monster had attacked him. When they finally got out of the wreck, they did not realize they had come out the wrong hole. they had staged their decompression bottles by their entry point, and when they come out and didn't see them, they thought someone had stolen them. They did have some gas, but despite that, they opted to head for the surface. Bernie Chowdhury (author of The Last Dive) Thinks it was because they knew he had survived a similar problem. Much of this is supposition. Chris died on the surface. Chrissie made it to the hospital, but he was pretty incoherent the whole time.