It's nigh on 17 years since I walked the Path but I remember the owner of one of the B+B's that I stayed at told me of an American couple who had expected the path to be like a Promenade. I suspect he was pulling my leg. On another occasion the days walk had been very precarious with parts of the path badly eroded and some quite stony places very close to the edge. When I finally got to my digs I was chatting to the owner and he told me of a young couple who had decided to walk that part of the Path, set out late and misjudged the difficulty. They lost the light and had to navigate by using the camera flash on their phones 😮
The couple you mention must have had their own boat as none of the tour boats would be there anywhere near darkness.
The story about the Americans was probably true.
A lifeboat run into Staffa a few years ago in a force 9 gale well after dark while heading to an emergency in the Sound of Iona.
The coxwain at that time was bit of a cowboy, if that is not insulting to cowboys.