Here is the section that addresses the randomness you speak of:
"For a given month, consider the collection of scores of evergreen stories (or non-evergreen stories). It is reasonable to assume that the observed collection of scores is only one of many possible ways the collections of scores might have occurred, i.e. the scores could have occurred with different values from what we observe. Rephrased as a thought experiment, if we had the ability to repeat the story submissions for a given month many times, we would expect the scores to vary from one attempt to the next. Let’s formalize this concept.
In the analysis that follows, we treat each measurement as a realization of a random variable. For example, in a given month, let’s say there are n evergreen stories, each with a score. We view the collection of scores in a given month as being generated by a sequence, X_1, …, X_n, of independent random variables."
The "randomness" I'm referring to is the answer why one submission got more points than another. It depends on multiple factors, such as time submitted, density of other submissions, current events etc.
This is the same reason your theory is flawed: assuming "independent random variables" only works if events have an equal probability of occurring.
