This question was originally just idle curiosity, without any reference to a claim being made. I flagged this as non-notable, and 3yahoo answers were added as references to the claim, which seems to be enough to warrant it being open.
At the same time there are other questions which are closed for not being notable, despite there being many more example of people believing/discussing the claim online.
This answer regarding what is notability states that:
A quick Google search showing several people writing about the claim should be enough to establish notability
This is the kind of murky, arbitrary guideline that is going to lead to a lot of people being upset when their question is closed for notability reasons yet other questions such as the one linked at the start of this question remain open.
When a claim is from an obviously famous source or takes up several pages of search results then there is no question of it's notability. It is less certain when the claim only has a few search results however.
I propose a guideline of having a set number of references to establish notability, when it is not obvious that the claim is notable. The exact number is a matter of discussion, but if a person can find say, 5 references (Yahoo Answers, forum posts, blog posts, wiki discussion etc) to different people online believing the claim, then that should be enough for notability.
The notability guideline exists so that original ideas are not challenged, which is reasonable. In which case showing a set number of other people believe a claim can allow the question being asked here. That can sometimes be hard to do and so I think putting a minimum requirement for references to show notability would be beneficial to the site.
It would also mean the guidelines to the site are less ambiguous and there is less room for subjective argument over whether something is notable or not.