The Rydberg matter which prof. Holmlid is talking about are atoms with circular orbitals similar to hydrino or Bohr model of atoms. They result from careful excitation of atoms in such a way, the electrons will remain on the verge of full ionization.
The formation of such an atoms has been described multiple-times, they just require rather complex magnetic traps devices and precisely tuned masers (i.e. sources of microwave spectrum, where these atoms absorb) for to prepare them in high yield.
This is true, but it doesn't seem that in his case this excitation occurs in a very careful manner; the formation of circular Rydberg states here seems to automatically happen as a result of a large production of low-l Rydberg atoms. InConditions for forming Rydberg matter - condensation of Rydberg states in the gas phase versus at surfaces (paywalled) Holmlid explains: