You can list a Calathea species as a synonym for a Goeppertia species if it has been reclassified as such, but you can't list the genus Calathea as a synonym for Goeppertia unless the entire genus has been reclassified. The genus Calathea still exists. Furthermore, some of the Calathea species have been reclassified as species of the Ischnosiphon and Maranta genera, so it certainly is not a synonym for Goeppertia in all cases.
Whoever added the cultivar entry for Calathea 'Freddie' should have included the species so that it could have been edited along with the species entry. The admins can't know whether a cultivar name should be reclassified unless the species name is present. I have edited the 'Freddie' entry and corrected the genus by adding the Calathea species as a synonym and the Goeppertia species as the accepted name.
Calathea (Goeppertia coccinea 'Freddie')
Edited to add that my changes to the name of the cultivar entry now make the final paragraph of your post somewhat incomprehensible, so anyone reading this and feeling confused should know that you were asking about the entry listed as Calathea 'Freddie,' which is now listed as Goeppertia coccinea 'Freddie.'