Nowhere does it say that Sweetgrass are a hybrid variety of turkey. True Sweetgrass breed true and produce only more Sweetgrass. Hybrid varieties won't breed true.
It is an interesting question "what is a hybrid variety?" There is not a standard of perfection for sweetgrass. And while sweetgrass breed true, you do not need any sweetgrass to produce one. So if you can derive a color by mixing other colors, is it a hybrid or not?
If you want to get sweetgrass from a standard variety (one of the colors in the Standard of Perfection), you start with royal palms, because they are black-winged bronze based (b1) and have the gray genes (cg). They also have Narragansett genes (ng). So royal palm is b1b1cgcgngng, and if you can just get rid of the narragansett genes, you will get sweetgrass b1b1cgcg. So how do we do that? One way would be to cross the royal palms with standard bronze. The resulting offspring will be bb1CcgNgng, where b is the bronze base, C is not white, and Ng is not Narragansett. If you cross these together, you will get many combinations. Some will get two bronze genes bb, and some will get two black-wing bronze genes b1b1, and some will get one of each bb1. At the white gene site, some will get two not white CC, some will get two gray cgcg, and some will get one of each Ccg. Finally, at the Narragansett site, some will get two Not Narragansett genes NgNg, some will get two Narragansett genes ngng, and some will get one of each Ngng (this gene is sex linked, so hens onlt get one gene at that site. Lets ignore that for now). So some birds will be bbCCngng, and be Narragansetts, some will be b1b1cgcgngng and be royal palms. Some will be bb1CcgNgng, and look like bronzes but carry recessive genes, and some will be b1b1cgcgNgNg, and be sweetgrass. Other combinations are also possible. But the relevant question is "are sweetgrass hybrids?" What about Narragansetts that were also produced without a Narragansett parent?
Food for thought, and also Thanksgiving!