I don't think you should have failed this audit, but not necessarily for the reasons you think. Yes, it appears to be a bad audit question1, and had I decided to review it, I probably would have failed. But since I am not familiar with haskell I probably would have skipped it. Personally, I don't think you should have failed it because I don't think you should have reviewed it.
I've said it before on other answers about audits in other queues and I'll say it again in a first posts queue, when reviewing, especially when reviewing answers, if you aren't familiar with the topic, you should skip.
From one of your comments (emphasis mine):
@GeorgeDuckett yes, the question is faded out at the bottom of the page. But you are asked to review the answer not the question. In some cases I would read the question but in this case the given answer is too short, low quality and doesn't explain any code given.
If you admit you review answers without even reading the question, then you need to rethink your review process. Sure, you can judge that post on the apparent quality and conformance to the guidelines, but you are not performing half of the review. How do you even know that the answer, even a high quality one, answers the question unless you look and understand the question? (In fairness, you do say you don't always read the question so it is not like you skip reading the question every time).
One effective way to make sure you only review posts you feel qualified to edit is to filter. Depending on the queue, the filter link has multiple options (to review questions only or answers only in the First Posts, or by type of close vote in the Clove Queue). There is also a tag box in all of the queues so you can specify the tags you want to see.
1 - My position on this being a bad audit question is that the original version shown before Gilles' edits was not an ideal Stack Overflow post. Yes, this was an OK answer that was made exceptional by the aforementioned edit, but since audits are supposed to be more obvious and given the lack of a body in the original, I don't see it being a slam dunk. That being said, it is great for educational purposes, so if they audits are every changed to being more educational then it would have been a good audit.
Yes, as someone who is unfamiliar with the technology as well, it appears to be a bad audit, but since you aren't familiar, you should have skipped.
When answering questions, it takes 5 extra seconds to review the question and the tags. That doesn't mean you need to take the question into account if it is clearly a bad (non-conforming) answer, but you also don't need to rush through the review either - that is the whole purpose of audits, to make you slow down and pay attention. If you learn to slow down and review everything as a result of this audit, then it actually did its job.