Ball teams do not always run true to form in a short series. In a season's campaign, class will tell; the best team will invariably win, unless disaster overtakes it. In a short series, some freak situation, same unusual play, may prove to be the turning point.
In all probability, when the 1919 series is over, a diagnosis of it will show that the final result was brought about by some unusual situation or freak happening that was given no consideration when the relative strength of the two clubs was considered.