This is partly right. FP approaches do tend to reduce the volume of mistakes, and reduce the kinds of mistakes you can make.

But that’s not because type errors are less likely. For dynamic functional languages they’re only less likely because the implicit contracts tend to be more general and the data structures tend to support a high degree of polymorphism.

The reason FP approaches tend to reduce mistakes is mostly that managing state is hard, and pure functions are easier to reason about.