These are old numbers, that are from before Halo 3 even released.
Read it carefully.
"Halo 3 is the concluding chapter in the Halo trilogy—an international award-winning action series that grew into a global entertainment phenomenon, selling more than 14.5 million games worldwide, logging more than 650 million hours of multiplayer action on Xbox LIVE."
It talks about the series itself, and it just so happens that if you add Halo Combat Evolved and Halo 2 together, the sales pop up at around 14.75 Million. "more than 14.5 million".