“Envelope expansion”......code words for “we got into a cg problem for the airspeed we were at”. Sounds like they got into trouble and couldn’t get the airplane back into positive control before they reached their abort altitude. The boldface for the test probably was if you decend to 5k feet and are do not have positive control of the a/c, then exit the a/c expeditiously....
Same type stuff we have at work, but our altitudes are a bit taller, as we are way heavier and faster. Having Martin-Baker seats helps.