As someone who gets paid to write code (nominally) and has also written a few novels, I don't agree with this characterization. From what I've seen of Copilot, it's more like having a text editor generate your next sentence or paragraph^[1]. The idea (as I see it) is that you might use it to generate some prose "boilerplate", e.g. environmental descriptions, and hack up the results until you're satisfied.
It's content generation at a fragmentary level where each "copied" chunk does not form a substantive whole in the greater body of the new work. Even if you were training it on other authors' works rather than just your own, as long as it wasn't copying distinctive sentences wholesale, I think there's a strong argument for it falling under fair use--if it's even detectable.
On the other hand, if it regurgitated somebody else's paragraph wholesale, I don't think that would be fair use. Somewhere in-between is where it gets fuzzy, and really interesting; it's also where internet commenters seem to prefer flipping over the board and storming out convinced they're right to exploring the issues with a curious and impartial mind. I see way too much unreasoned outrage and hyperbolic misrepresentation of the Copilot tool in these threads, and it's honestly kind of embarrassing.
As far as this analogy goes, it's worth noting that the structure of a computer program doesn't map onto the structure of a piece of fiction (or any work of prose) in a straightforward way. Since so much of code is boilerplate, I would (speculatively, in the copyright law sense) actually give more leeway to Copilot in terms of absolute length of copied chunks than I would for a prose autocompleter. For instance, X program may be licensed under the GPL, but that doesn't mean X's copyright holder(s) can sue somebody else because their program happened to have an identical expression of some RPC boilerplate or whatever. It would be like me suing another author because their work included some of the same words that mine did.
^[1] At least one tool like this (using GPT-3) has been posted on HN. At this point in time I wouldn't use it, but I have to admit that it was sort of cool.