The querent stated that they believed the knock to be Morse code, ".././...", and two answers that essentially said that it was instead "..-/..." and gave a reasonable translation were deleted as "not an answer". Maybe I'm missing subtext, but I've seen a number of good answers on the site which essentially go "No, you're hearing/reading that wrong. It's this, which means the answer is this."
This kind of answer is sometimes known as a "frame challenge": instead of answering the question under the OP's misapprehension, it challenges the framing of the question by proving the OP's assumptions wrong. An example of this can be found here: the question asks why Snape killed Harry Potter's parents, and the top answer (score +14/-0) explains that he didn't.
Things get a bit more sticky when someone attempts to post a frame-challenge answer which is itself incorrect. If someone had asked why Voldemort killed Harry Potter's parents, and someone else had answered saying that in fact it was Snape who killed them, that answer would certainly have been downvoted and possibly deleted by reviewers.
According to Is deleting really wrong answers OK according to the rules?, answers which are simply wrong should generally be downvoted and/or commented instead of deleted. One reason for this is that wrongness can be difficult to judge without specific expertise, and moderators/reviewers shouldn't always have to need that expertise in order to know whether or not to delete a post.
Get to the point, Rand ...
So what about these specific answers, the ones that state the Morse code in Stranger Things was
..-/... instead of
.././...? Well, if they're right, then they certainly shouldn't be deleted, as they provide a valid frame challenge and the correct answer to the question. If they're wrong, then they could arguably be deleted, but they're still attempts to answer the question and we don't usually delete answers just for being wrong.
Are they right or wrong? I don't know; I haven't watched the show.
Had all five of the delete-voters watched enough of the show to be sure these answers were wrong? I don't know, but one of them has posted an answer here explaining his delete vote without reference to wrongness of the answer, saying that there's "no basis for the morse they were suggesting" and the answers "lack [...] any form of details". (If the answers are right, the "basis" would be simply watching the scene in question carefully, and I'm not sure what further details would be required.)
Why does the same answer keep getting posted again and again? Unless it's the same person trying to share their interpretation with us three times (unlikely considering the different usernames and avatars), it seems to be either a common misconception or the actual correct answer.
As a delete voter on both posts, I will give some insight into why I voted to delete both answers (well the second was obvious considering I'd deleted the first).
When should I vote to delete an answer?
You may vote to delete answers in the following cases:
- The answer is extremely low quality: There is little to no scope for improvement
- The answer doesn't attempt to answer the question; it may be a comment or a separate question altogether.
It is my opinion that the answer fell under the first bullet point, given that there was no basis for the morse they were suggesting, as indicated in my comments above, and the lack of any form of details the answerer should be providing.