Reading the post again, it seems to me it isn't about raw speed in producing a finished product; it's about the ability to explore a problem space by writing small throw-away trials, before you know how the result should look. Physical speed is just one part of this; I'd say it's really about fluency. Do you use code as a medium for thought and expression, or do you have a separate step where you translate your ideas into code from some other form?

This is a real distinction I see even in experienced developers, and in that case I think it's more a matter of habit and practice, rather than skill. Some of my co-workers have an ingrained habit of sitting down at a REPL and trying out several ways of doing things, whenever they're thinking about a problem. Others have apparently never tried this way of working, even though they are probably quite capable of it.