Yeah, that’s because grapefruits are pomelo and orange hybrids. And it’s the only American native citrus. The parent species were brought to the Americas from Asia. They escaped from plantations, crossbread in the wild (in Barbados) and that’s how grapefruits were born.

Also, pomelos are one of the few comercial citruses that are not hybrids, it’s a botanic species (unlike oranges, lemons, limes and tangerines)