That's incorrect. It applies to unaided processes; "randomness" (as opposed to merely being "unaided") is used merely as an educational tool to dumb down the mathematical discussion.
Which, as you can see by the sheer volume of drivel posted already in response to that math, was a minimum required intellectual tool.
The word random has a well understood meaning and is fundamentally relevant to the math you presented. The words "aided" and "unaided" are in fact words that are uniquly used to replace the normal "random" used when modeling processes with those functions. Since you have little in the way of knowledge regarding the actual biological process that occurs in reality,; you can't possibly represent the real process with random linear constructions.