It's not that this is wrong, so much as it is a childish oversimplification. No, Mexicans, blacks, and Asians don't like or get along with one another in regions of the country where 2 or 3 of those groups are present.
They will, however, readily form alliances in cases where it's beneficial to do so. Look at a college campus and note how the student associations for Hispanics, blacks, and Asians are all in lock-step with one another, denouncing white supremacy, toxic masculinity, "Nazis" (ie any white person not ashamed of their heritage), "Zionists" (ie any Jew not ashamed of their heritage), etc.
Yang being Chinese isn't a hindrance at all, and still an advantage over being white like Sanders, Biden, Buttie, Robert Francis O'Rourke (a fake Mexican who looks like a
Thomas Nast caricature of an Irishman), Gillibrand, and Klobuchar.
If he were nominated, rest assured that minorities would still support him overwhelmingly simply because he has a D next to his name.