That's a good point! It makes a good story, but it's hard to believe the visitor didn't speak up when the confusion became obvious, which was right away. I could believe it more if the visitor didn't speak much English at all, as they might not have known other ways to phrase what they wanted, but that didn't seem to be the case here.
I work in a place with a lot of international people who have varying grasps on English, and there have been some interesting misunderstandings. The one that first comes to mind is when it was 4:45pm on a Friday (of course) and I had to help a person who was using a machine we were responsible for. I'm trying to think of a good analogy for what he had done... there is a plastic sheet you're supposed to put through the machine, but you need to peel the piece of paper off the sheet first, and he hadn't, and just ran the whole thing through. Like trying to use something without removing the safety seal first, maybe. And in his case, it revealed a fundamental misunderstanding of the whole technique, because the piece of paper wasn't just packaging, it was actually a vital component of his experiment, which had now been ruined by going through the machine. I think I had to lay the mutilated, waterlogged paper back on top of the plastic sheet and show it to him, to get across what had happened. He got very quiet after that.