In 22w19a, when I reflected ghast fireball, it just passed through the ghast and exploded, making terrain destroyed. However, the ghast did not get any damage. Also, the fireball cannot make some fire-immune mobs (just like zombified piglin) hostile. (For those mobs which can hurt by fire (e.g. piglin or wolf), ghast fireball can make them hostile. ) Meanwhile in 22w18a, these situation didn't exist.
Code analysis by apple502j can be found in this comment.