According to the announcement, those numbers came from the "distribution figures of the package version and sales figures of the downloadable versions" as of March 14th, 2022. With those sales numbers, Elden Ring smashed a bunch of other records associated with Souls-type games. FromSoftware's previous release, Sekiro, sold 2 million copies in 10 days, and it took four years for Dark Souls 3, the best-selling game in the series, to reach 10 million units sold worldwide. Based on how well it's doing, it seems apt to compare Elden Ring to Pokémon Legends Arceus, which sold 6.5 million copies in seven days — and that's a game from a franchise that already has a massive following. 

FromSoftware developed Elden Ring with help from A Song of Ice and Fire creator George R. R. Martin, who wrote the overarching mythos for the game that features Lovecraftian creatures and dragons. At the helm of the project was Hidetaka Miyazaki, known for creating the notoriously difficult Souls games, as well as directing Bloodborne and Sekiro. It was supposed to be available back in January but was ultimately released on February 25th for the PlayStation 5 and 4, Xbox Series X|S, Xbox One and PC via Steam.