I think the mistake here is that you think “purposeful study” and “pick up metaskills as you hack away at your project” are not both examples of (potential) del

I think the mistake here is that you think “purposeful study” and “pick up metaskills as you hack away at your project” are not both examples of (potential) deliberate practice. What makes either one deliberate or not is whether you make a point to focus on how well it was done, how it achieved goals (or not) and how to improve. That’s the deliberate part and that’s the part that makes the difference and is missing by default. As long as you’re constantly evaluating and making attempts to improve, it doesn’t matter so much in what context you’re doing the thing, whether it be for fun, for learning, for work, or whatever. “Practice” simply means you’re actually doing a thing as opposed to studying it theoretically. Though I think many people have a habit of reading into that word the notion that what you are doing is a throwaway or has very low expectations of success or importance. But keep in mind that what a doctor does every day is called “practice.”