A more general response than to that specific referenced post.
"Take no prisoners" approach (not recommended)
The key word in "duplicate question" is "question", not "answer". Ideally, it would be nice to collect answers to a specific question in one place. On this basis, some people have said that if the question already exists, new answers should be directed there even if the existing answers don't answer the new question.
If the original question is old, chances are slim that it will be attracting new answers. How do you get new answers there?
- Edit the old question to improve it and expand it to include the new question, which bumps it into the active questions list.
- Post a bounty to attract new answers. New user with no rep? Out of luck.
This approach sort of sucks if there is not already a solution to the new question.
"Benefit of the doubt" approach (recommended)
Identifying duplicates serves two purposes:
- pointing the OP to existing answers that may solve the problem
- avoiding duplication and clutter on the site
The site priorities are:
- Get (good) questions answered and attract new (good) answers
- Curate the site
The first priority is way higher than the second, and we don't need to nit pick over how similar two questions are in order to accomplish the second priority.
Duplicate questions are rarely duplicates, they're "similars"; similar question and/or similar solution. If the existing answers on the original question don't answer the new question, then pretty much by definition, it is not a duplicate question. Identifying, in the new question, the shortcomings of the existing answers clarifies what makes it a different question.
Whose opinion counts as to whether the question is a duplicate? Initially, it doesn't need to matter. If the OP says the existing answers don't work, leave the question open to attract new answers, even if you're convinced that it's a duplicate.
After the question has attracted whatever answers are forthcoming (say three or four days), then assess the need for any site cleanup. If warranted, at that point, the question can be closed as a duplicate, along with the additional answers that probably would not have been posted had the question previously been closed. Or the question and additional answers can be merged with the other question. What if you end up with some duplicate answers? Super User will survive.
There might even be a surprising answer that illustrates that it really was a different question after all. It could happen.