My understanding is that CA is slightly acidic in the bottle - that's what keeps it from setting. When it contacts anything that neutralizes the acidity then it is capable of setting (if moisture is also present). Since baking soda is a base it quickly neutralizes the acid in the CA and the gue sets rapidly. It's good to use on an some plywoods (spruce?) that are acidic and therefore resist CA.

... at leasts that's the theory as I understand it.