The scope is much more limited in his case. When the problem space is super narrow and the base language is your whole environment, writing correct code in a big batch is not that hard. On the other hand, dealing with flask and basically the whole stack of everything web at the same time is a different kind of challenge.

Writing code by hand isn't too bad, especially with a good language like LISP. I don't think it requires too much extra effort, just more attention and care as to not make syntax mistakes. With near-instant compile times and auto-linting, we sort of lose the ability to auto-vet code before inputting it.