mixed-blood vs someone

mixed-blood and someone both are nouns.

Word	Noun	Adjective	Verb	Adverb
mixed-blood	Yes	No	No	No
someone	Yes	No	No	No

As nouns, someone is a hypernym of mixed-blood; that is, someone is a word with a broader meaning than mixed-blood:

mixed-blood: a person whose ancestors belonged to two or more racial groups
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of mixed-blood include individual, mortal, person, somebody, soul.

mixed-blood (noun)	someone (noun)
a person whose ancestors belonged to two or more racial groups	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential