That's kind of a retarded way to put it. CS has no way to change fov, so you have to 'stretch'. It's a work around because valve doesn't have a very good engine.
90, 100 and 106 are the only fov you can choose from, but setting 4:3 stretched to 16:9 you can have 90 fov (actually 90 horizontal fov, 74 vertical fov) but stretched to 16:9 which means it's about 25% wider (didn't actually run the math, just an approximation).