Unless your coupler was so far out of adjustment that it simply was too big for the ball, you likely had what's known as a "false hitch". That's when someone snaps the coupler down thinking it's latching around the ball and it's not.
More common than you'd think, and more so among experienced RVers that sometimes tend to get complacent about such things. Best to check for true couple by using the jack to attempt to lift the tongue after coupling is complete.
But like a previous poster, not sure how this helps since it sounds like you've already had some sort of catastrophe...