Lots of materials in inspector
The material list in the MeshRenderer represents the number of times the renderer needs to tell the graphics API to switch textures/shaders/materials because of the way they are layered. (Hence the 5 SetPass calls).
It has 2 materials but it needs to switch between them 5 times, in this case, because it needs to draw head parts, then the shield, then body parts, then the sword, then more body parts.
This is the way it will work anywhere, with any engine. Not just Unity. Not just Spine.
There are many ways to optimize this so you get fewer draw calls, but it really depends on what you need. 200 vs 500 calls may be worth a optimizing. 2 vs 5 is a waste of time (ie, don't worry about it. that will not slow down your game in the slightest, even on mobile.).
But there are ways like generating a big texture at runtime so even if you need a mix of textures, you can have the characters just use one texture so it never needs to switch materials. Again, this is only worth doing if you need it.