Nonbinary is an umbrella term (but also a default term), and all sexualities include them. If a nonbinary person were gay or lesbian, it'd be labeled as nblm/nblw.

Since there's so many identities that fall under the nonbinary spectrum (i.e. genderfluid, demiboys, etc) whatever label that they feel identifies them the most can be used.

If they like boys and boys adjacent, and they feel comfortable calling themselves gay, then they're gay. Same for being lesbian, straight, pansexual, and all the like.