Randomness is lumpy

Randomness is lumpy. Can you imagine anything less random than a bunch of trees all growing in a matrix each 2 metre apart, perfectly 2 metres apart. Or, if you dropped a handful of jelly beans and each one fell, perfectly 3 cm apart from each other.  Unlikely, and not "random". So why are we so surprised in public health (and life in general) when we see a "cluster"  (a time space aggregation) - isn't this what we should expect to see?   But then if we believe there is a cause behind everything is anything truly random or do we just not the reason determining the outcome.   See this nice article at 3quarks daily for more.