Post: #2

You are correct.

brain_dragon inherently breathes fire. This acts like an explosion spell, but it is not. When a dragon attacks a player, it will always breathe fire first. As it isn't actually a spell, it won't be reflected or trigger any magical protection.

If you wanted a dragon to cast a reflectable explosion, you'd likely want to give it the brain_monster and force it to cast explosion on attack (potentially on a cooldown)