Of course it's quality over quantity. 20 lines is not a lot and I think that's the point; whether you're measuring LOC -- which is a well-established bad metric -- or something equally spurious (e.g., semicolons per kilobyte hour) the fact that a very low number was chosen is telling. LOC is just used as a proxy here for something quantifiable; accuracy is somewhat irrelevant.
Writing is not the best analogy -- because of the typical churn-edit cycle -- but to use your example, of course reaming out pages of text in one day will, on average, be of a lower quality than a virtuoso author who carefully chooses his/her words and maybe produces, on average, a paragraph a day. If you were to tell a layperson that a good writer can output a paragraph a day, they'd probably find that counter-intuitive because it's such a minute amount; "Surely anyone can write a few sentences in eight hours? Even I could do that!" They're making the same false-entailment, without seeing the craft that went into those paragraphs/day, or realising that there will be days when said author writes nothing and others where they're in the zone and write an almost-perfectly-formed chapter. That doesn't stop "paragraphs/day" from being a bad metric, nor does it imply that anyone who writes a paragraph a day will end up with anything good.
Writing is not the best analogy -- because of the typical churn-edit cycle -- but to use your example, of course reaming out pages of text in one day will, on average, be of a lower quality than a virtuoso author who carefully chooses his/her words and maybe produces, on average, a paragraph a day. If you were to tell a layperson that a good writer can output a paragraph a day, they'd probably find that counter-intuitive because it's such a minute amount; "Surely anyone can write a few sentences in eight hours? Even I could do that!" They're making the same false-entailment, without seeing the craft that went into those paragraphs/day, or realising that there will be days when said author writes nothing and others where they're in the zone and write an almost-perfectly-formed chapter. That doesn't stop "paragraphs/day" from being a bad metric, nor does it imply that anyone who writes a paragraph a day will end up with anything good.