If 59% of 13-17-year-old girls are playing video games, as Pew recently reported, then why is it assumed that teen gamers are mostly boys?

If 59% of 13-17-year-old girls are playing video games, as Pew recently reported, then why is it assumed that teen gamers are mostly boys? Of the teen girls who say they play, 47% say they never play online, and 27% say they never play with someone else in the same room. Girls who do play online are far less likely than boys to talk to other players, with only 28% using voice chat, compared to 70% of male teen players. So teen girls are playing—but they’re staying silent. (Kotaku)