I didn't get that from the talk. What the author meant (I'm also extrapolating from advocates of dynamic languages) is that quality increases with iteration. By changing and running your program, you can find edge cases you hadn't thought about and modify it to make it testable, modifiable, easy to inspect/visualize, etc. An environment that reduces friction required to tinker with a programs allows you to make them robust too - if you so wish. If you just want to play, then you're free to do that too (and the creative process benefits from being able to do so).

I'm not advocating for only using this workflow, ideally we could add types too. Compilers can enable an iterative workflow (Elm comes to mind), but I find myself sprinkling types as I go exploring how my program will accomplish the task (TS without strict).

The pendulum has swung to type-everything-first and I'm not sure it's the silver bullet we're looking for.