It "feels" important to me that the word μύθος mythos "myth" just means a "tale, story, narrative." Myth implies to us specifically stories about the gods, but I don't think that's what Epicurus intends in his "then you will escape a long way from myth." To paraphrase, you will be far from talking fiction if you follow the Canon etc.
But, here are two of the relevant sections of the Letter to Pythokles:
Quote[87] "For in the study of nature we must not conform to empty assumptions and arbitrary laws, but follow the promptings of the facts ; for our life has no need now of unreason and false opinion ; our one need is untroubled existence. All things go on uninterruptedly, if all be explained by the method of plurality of causes in conformity with the facts, so soon as we duly understand what may be plausibly alleged respecting them. But when we pick and choose among them, rejecting one equally consistent with the phenomena, we clearly fall away from the study of nature altogether and tumble into myth. Some phenomena within our experience afford evidence by which we may interpret what goes on in the heavens. We see how the former really take place, but not how the celestial phenomena take place, for their occurrence may possibly be due to a variety of causes. [88] However, we must observe each fact as presented, and further separate from it all the facts presented along with it, the occurrence of which from various causes is not contradicted by facts within our experience.
The word used in 87 translated as "facts" is φαίνω and means "that which appears to the senses." The assumptions and laws are arrived at by reason and are man-made. Epicurus is saying we need to not be lured in by fancy arguments or stories or what we think are worthy but by what we perceive by our senses. And then...
Quote"A world is a circumscribed portion of the universe, which contains stars and earth and all other visible things, cut off from the infinite, and terminating ... in an exterior which may either revolve or be at rest, and be round or triangular or of any other shape whatever. All these alternatives are possible : they are contradicted by none of the facts in this world, in which an extremity can nowhere be discerned.
So, with that last part, I can't rule out the articles authors thesis. Epicurus does say all the alternatives are possible or permissible or allowed. But I want to delve into that a little deeper in context and the original.