Duplicate here has two possible meanings:
- identical question has been asked,
- different question, but identical cause or resolution
There are plenty examples of the first, and these questions are usually closed as duplicates, and deleted, or merged, if there are worthy answers.
The second case is more interesting as they are different questions, but answering them is actually a duplication of effort already applied to previous questions. Sometimes, if they generate answers, they provide insights that the original did not have, but this is usually not the case. For your question, the only answer provided nothing new.
Additionally, the second case is interesting in one other respect: they provide different pathways to access the answer. Consider this question of mine, Automatically including custom stylesheet with notebook, closed as a duplicate, but it has enough unique characteristics that it remains undeleted. This is a good thing for finding things via search engine. StackExchange's goal is to provide good answers that are easily accessible, so every pathway helps.
Lastly, we have a limited number of close reasons available to us, so there will be some ambiguity in the use of any of them.