I won't repost my whole comment here, and there's always room for discussion if someone knows the internal politics, but the basic question has been asked in the past. In short, the name comes from the Bight of Benin, which itself took its name from the kingdom of Bénin. It is not therefore a direct appropriation. Dahomey was a Fon state, and Bénin was (and still is) an Edo/Bini one with Yorúbà cultural ties, so there was no direct connection historically except that mediated by Oyo or other Yorúbà states. The name change itself had more to do with de-centering the colonial past and the Kingdom of Dahomey in the new dispensation of the mid 1970s.