The secret sauce seems to be ultra-dense deuterium, "D(0)" whatever that means. Looking through the author's other papers, it looks like he's claiming to have made metallic hydrogen, which would be a Nobel Prize right there.
If he can demonstrate this, then fine
... he's a super genius.
Perhaps he's making flakes of Rydberg matter, floating in a near-vacuum.
(If I understand it correctly) this is matter where the individual atoms have been NEARLY ionized, by pumping an electron up to ALMOST, but not quite, the energy needed to free it from the atom, leaving an ion. (You can do this with a laser tuned to the energy difference between the ground state, or the state the electron WAS originally in, and the state you want it in.) If you get the electron into one of the high, flat, circular orbitals, it looks almost like a classic Bohr atom (earth/moon style orbit), and the state lasts for several hours.
Atoms in such a state associate into dense hexagonal clusters. (19-atom clusters are easy and heavily studied, and clusters of up to 91 atoms are reported.) The electrons bond the atoms by delocalizing, forming a metallic, hexagonal grid, similar to a tiny flake of graphite sheet. You can't make them very big. (There's some issue with the speed of light screwing up the bonding stability when the flakes get too big.) But you can make a lot of them, creating a "dusty plasma".
So hitting gas with the right laser pulse could end up with lots of flakes of this stuff, with deuterons held in tight (dense!) and well-defined flat hexagonal arrays by a chicken-wire of delocalized electrons, with zero (or tiny) net charge, floating around in a near vacuum and suitable for all sorts of manipulation. (Like slamming them into each other, for instance.)
Now how this interacts with substituting muons for electrons (something analogous to an impurity in a semiconductor crystal?), missing or extra electrons (ditto?), occasional oddball nuclei (again ditto?), or perhaps how it might generate muons when tickled by appropriate laser pulses, all look like good open questions for active research.
The point is that it's pretty easy to get these long-lived, self-organized, high-density, stable regular geometry, crystal flakes of graphite-like deuterium floating in a near vacuum, where you can poke at them, without any pesky condensed matter to get in the way.
Easy as in maybe you can do it on a desktop with diode lasers, producing "maker" level nuclear physics experiments. B-)