Unitarians don’t claim to be “Christians” in any ordinary sense. No (small “o”) orthodox Christian denomination (Presbyterian, Baptist, Roman Catholic, Methodist, Lutheran, Eastern Orthodox, etc.) will call Unitarianism Christian either.
Christians all acknowledge one God in three Persons, the holy Trinity (Father, Son and Holy Spirit)...Unitarians by definition (hence the name...) do not.
Not trying to dis anyone, its just a fact.