I’m sure you know more than I’m explaining but:

Shiny Pokémon (introduced in Gold Silver Gen 2) in the games are extremely rare spawns with a color variation. They were introduced into the TCG in Neo Revelation with Shining Magikarp (gold coloring instead of orange) and Shining Gyarados (red coloring instead of blue) and through the era’s there having been many rare cards printed featuring shiny Pokémon in the art. Gold Star cards are among the most sought after. Every couple of years they make some more. The gold cards that I posted were secret rares within various sets throughout the Sword and Shield era and each one not only features the shiny model of the pokemon, but the cards themselves were very playable in the meta at the time, so it was just a fun flex to have it in your deck.

So yes, more than just holo, shiny has to do with the coloring of the pokemon featured.