[Skysworn] question to replace my previous question about the wrong book..

I've just started reading the cradle series and I'm really enjoying it. One thing I think I've perhaps misread or misremembered is in chapter 9 (page 150?)

Where it says that Lindon had to help so he "gathered a dark fireball between his palms" but doesn't he only have one arm at this point because his new arm "was still in the process of being created"?

Hopefully someone can clear this up for me!