I like to think their choice of language definitely helped, but I'm also pretty biased :)

In particular, I've found that having an expressive type system makes it easier to develop and communicate this kind of mental model, as well as to maintain a close mapping between the concepts you use to understand the system and the code itself. I'm convinced that this is a powerful approach that can be incredibly effective and is hard to reproduce in "normal" languages, but it's hard to state this too confidently since it is entirely based on my own qualitative experience with programming.