heterosexual person vs someone

heterosexual person and someone both are nouns.

Word	Noun	Adjective	Verb	Adverb
heterosexual person	Yes	No	No	No
someone	Yes	No	No	No

As nouns, someone is a hypernym of heterosexual person; that is, someone is a word with a broader meaning than heterosexual person:

heterosexual person: a person having a sexual orientation to persons of the opposite sex
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of heterosexual person include individual, mortal, person, somebody, soul.

heterosexual person (noun)	someone (noun)
a person having a sexual orientation to persons of the opposite sex	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential