You don't know that. Over infinite iterations, a process can appear to be random for a set of variables.
i.e. a dice appears to be random, because we can't accurately control its throwing and environment parameters.
i.e. a drop appears to be random, because we can't raid with 25 gnomes or 25 mages.
therefore, there is no real legal way of knowing for the user on whether it's TRULY random.