Well, in the parent case X might have been "count the unique lines in a file", Y might have been Python because they were interviewing for a Python job, and Z might have been "cat | sort | uniq".

What the interviewer wants to know in this example is whether the author understands Python and file IO and data structures. Sure, you'd use the Unix pipeline in a production setting because it's better tested and faster. But in an interview context, that doesn't tell you whether the candidate is more likely to store item counts in a list or a dict, and that's what you're really trying to dig into.