I think both meanings are plausible in this context. "Racially mixed" could reasonably suggest "mixed race", and "mixed race" always means multi-racial in Engli

I think both meanings are plausible in this context. "Racially mixed" could reasonably suggest "mixed race", and "mixed race" always means multi-racial in English. Mestizo is a similar term. The author could have chosen a clearer phrasing to avoid this problem.