Sounds about right.
I'd like to see numbers for inexperienced devs and devs working on somebody else's code, though.
EDIT: Oh, this is interesting. The full paper breaks down where the time goes. Turns out coders do in fact spend less time actually working on the code when using AI, but the time spent prompting, waiting on the output and processing the output eats up the difference. They also sit idle for longer with AI. So their forecasts aren't that crazy, they do work less/faster with AI, but the new extra tasks make them less productive overall.
That makes a lot of sense in retrospect, but it's not what I was expecting.