First screenshot: you do more damage with a fireball because your two weapons give a bonus on Magieschaden. Your magic spells also benefit from this bonus! Hammer gives you +14 and Schwert gives you +9. In total, your magic damage is augmented with 23. Fireball is magic damage. The difference between the damage you do here and the damage you do when you are Unbewaffnet, is not 23, but that is because the base damage plus the bonus then gets a % modifier (e.g. from your intelligence).
Second screenshot: you do more damage because your bow gives a bonus to Fernkampfschaden (ranged damage). Fireball also benefits from this bonus because it is a projectile.
Third screenshot: there is no bonus on this weapon so you do "normal" base damage as with the Unbewaffnet character.
So yes, your magic spells benefit from bonuses on weapons. It has nothing to do with the fact that the weapon does magic damage, it's the bonuses that have done this.
Hope this clears this up?
