Who do you mean by 'they'?
Yes, plenty of people self-identify as mixed race, but there are others who consider it inaccurate, if not offensive, because there's no such thing as race, so there's nothing there biologically, as the term implies, that a person can have in only partial or mixed form. 'Dual heritage' may be a mouthful, as
maomao says, but the number of syllables isn't the only criteria in play as far as appropriate terminology goes, and I know people who prefer it.
Anyway, it's not really that pertinent in the present context. I was only being mildly satirical in response to someone whose attempt to prove his internationalist credentials includes a reference to his extensive property portfolio