To their credit, the mechanism sounds plausible. Inclusions trick the atoms into getting closer together? Sure, why not. If that showed up in science fiction I’d probably stop reading… and check if anyone had actually tried that yet.
(Off-the-cuff, I presume we can’t just twist or bend a metal in lieu of obscene pressure. Too many zeroes.)
But the fact nobody’s immediately slapping their forehead, recreating this ASAP, and breathlessly declaring a new age of etc., is a strong indicator it’s overselling an interesting outcome. Just like that reactionless thruster from a few years ago. The goal is highly desirable, and the argument for why it ought to work sounds perfectly reasonable, but the universe doesn’t run on argument.
It’s normal for crystals to have changes in their size when you replace atoms.
The material they talk about here is a metal oxide, not just a metal. These are much more brittle than metals but they can still take some minor squashing or stretching (like ceramic bowls ringing). You’re correct that this takes a lot of pressure to sustain.
It’s a bit too soon to say no one has recreated it quickly, the paper was only uploaded a week ago. I’m also skeptical but we should see some responses from other physicists soon.
This article also has some more doubts about the material itself
Great article. It ends with: "If this is real, we’ll know within a week.”