The discussion on the forum the pics came from is centered around how and why as you would expect. One of the contributors, a pilot, had this to say about hail in general :
Hail has been known to get ejected from the tops of thunderstorms and blown downwind of them clear of the body of the storm. If it has time and conditions are right it will refreeze making it dry. You can be flying along in clear air 10 miles downwind of a 60,000'+ thunderbumper and hit hail unpainted on airborne weather radar. Then you do the chief pilot carpet dance explaining why you didn't go around it by 20 miles.