The sun is also at a temperature of millions of degrees. At these temperatures, there is no such thing as chemical bonds, and so the rules with hydrogen from the article don't apply.

interesting, is this a sub-field of physics ? high temperature physics or something ?

Plasma physics I guess, plus magneto hydrodynamics, plus GR for really heavy stars.

dank u

High energy physics, yes.

danke schon

No, it's a plasma. The high pressure in the article is a way of getting to a part of the phase diagram of that particular crystal where the superconducting transition happens at a higher temperature.

How about the metallic hydrogen that might exist at Jupiter's core?

it's probably too hot in there, but I wondered the same thing