It's difficult to know whether to categorize this claim as a myth or not because atheists do commonly describe the universe as "random" in some sense, but that doesn't make the claim true. Where the problem lies is in how religious theists who make or believe this claim misunderstand or misrepresent what random means. When used correctly, this can be a correct description of many atheists' positions. When used in the manner that many theists seem to intend it, it's incorrect and thus a myth.
Read Article: Myth: Atheists Believe in a Random Universe, Not an Ordered & Orderly Universe
Chaos theory says that perfect chaos is the same as order. If the universe ends as a big crunch or heat death, either way, it is a perfectly ordered end result.