Good question. I always thought that the name was associated with the location since the country is located just slightly south of the equator.

probablemente porque era una colonia española

Yes, in Equatorial Guinea they do speak Spanish. Also French is widely spoken as well as Portuguese in some parts.

Yes, they do speak Spanish. I visited Equatorial Guinea this past August. A lot of people who work in the hotels or other service based professions have some understanding of English.