I would suggest consulting philosophy, anthropology, or literary criticism. However, if you consult Merrian Webster, the first two defintions approximate the way the term "myth" is used in scholarship.a widely held but false belief or idea.
If something existed, its not false.......
Levin saying something didn't exist, that did no matter how limited, however would be a myth, and a false belief or idea. Think I understand the definition fine
a usually traditional story of ostensibly historical events that serves to unfold part of the world view of a people or explain a practice, belief, or natural phenomenon; parable, allegory… See the full definition