The article is from 1989 and this used to be one of the common writing styles back then. Of course, times have changed now and (at least to my ears) "they" sounds more natural than "she" in the current century.
Tabletop RPG books c. 1989 were doing all kinds of stuff with generic pronouns. I believe Vampire (1991) primarily but not exclusively used "she". Other games would use "she" for the GM and "he" for players, stuff like that.
