alt Hacker NewsThe training data includes plenty of examples of labelled good and bad code. And comparisons between two implementations plus trade-offs and costs and benefits. I think it absolutely does "know" good code, in the sense that it can know anything at all.
There does exist some text making comparisons like that, but compared to the raw quantity of totally unlabeled code out there, it's tiny.
You can do some basic checks like "does it actually compile", but for the most part you'd really need to go out and do manual categorization, which would be brutally expensive.