Multiracial and multiethnic both fall under the category of bicultural identity. I’m still trying to figure out how they differ.
Is it merely a matter of passing? Multiracial individuals tend to be more visually identifiable than multiethnic ones. That theory might hold, until you run into the one-drop rule, the law turned social “common sense” that anyone who is part black is all black.
Is there a stronger sense of duality for multiracial individuals than multiethnic? Again, there’s an assumption that race is a larger category than ethnicity, like saying “Oh, if you’re Vietnamese and Indian, you’re still Asian.” The explanation, in a sense, makes multiethnicity more normal than multiracial.