It's not possible that clicking the operate jetway would cause the GSX customization page. However, since the Operate Jetways is option 6 and Customize parking is Option 7, it's possible you might have clicked on the mouse and for some reason the mouse didn't registered correctly. Does it work using the number 6 on the keyboard ?
Nothing to do with GSX, of course, since mouse and keyboard handling of the menus are done entirely by the sim.