Okay first of all, we have no idea if Xochitl Gomez has even been cast as America Chavez. The role is undisclosed, but sure it's likely that's who she's playing.
Second, when has America ever been considered black? I really do not recall her ever being referred to as such. Never knew her as Afro-Latino.
Third, this is the same Twitter people that got mad about Hallie Steinfeld allegedly being considered for Kate Bishop because "Kate is Asian", even though that's never been true, it's kinda racist to just call her Asian without specifying her nationality or ethnicity, and Steinfeld is part Filipina.