If i read that correctly, this code line says if you do NOT have the Pyromaniac perk, and you attack with fire and your ammo is dragon's breath, then you do 1.25x dmg. To me this does not say you don't get a dmg bonus WITH Pyro.
Unless == means equals and != means NOT equals. If that's the case, then this was written specifically to exclude gecko breath ammo from Pyro's bonus dmg. That means a developer thought about it and said, nope, you should not get a dmg bonus from these fire-based shells even though you have the perk that is supposed to give you bonus dmg to fire-based attacks. We may all find that weird, but we don't all think alike.