The info was two-fold.
First, that the Shield became the top selling commercial pistol in the world for the last period (6 months?) from which numbers were pulled within the industry.
Second, that the sales of the Shield, in the short time it's been available, has broken every sales record of the company, which isn't the same thing as the total number of units ever sold compared to any other particular model over a decades-long record.
If the Shield is around for as many decades as the venerable "M10", I wouldn't be surprised if the total number sold, over the span of another several decades, might eclipse that of the revolver.
FWIW, last Fall we were told in a Glock armorer class that in the time their G43 has been on the market, it had become the fastest and hottest selling Glock model.
I don't know what the numbers of the XDs might be, because I'm not a Springfield pistol armorer and thus haven't had any inside info/trivia offered by a rep, tech or armorer instructor. Ditto the Kahr or Beretta lines of little pistols.
The allure and sales of the diminutive plastic 9's have been pretty hot for the last couple of years, though.