Where did you come up with that definition of infallibility? Nothing on faith and morals and speaking ex cathedra?
Speaking extra cathedra is to act like the old English kings did and to pronounce what has always been “law.” or as a Chief Justice might in deciding what is “constitutional.” I am as leery of the Ultramontanes as I am of the Gallicans,although not ashamed to call my self a papist.