What does "guinea" mean here?

The "Partridge Dictionary of Slang" has an entry for "Guinea people" as a synonym for "Jamaicans with strong sense of African identity".

In addition, p214 of the Jamaican English Dictionary, you will find this entry:

GUINEA-MAN sb; cf OED 2 1830 → A man born in Africa.
a. 1818 Lewis (1845), "On hearing of this fresh instance of devilism, I asked her mother 'how she came to have so bad a daughter, when all her sons were so mild and good?' 'Oh massa', answered she 'the girl's father was a guinea-man'.

Other entries (like Guinea ship for instance 'a ship bringing slaves from Guinea (Africa)') suggest that the Jamaican meaning of Guinea is Africa and that a Guinea man is a slave born in Africa (as opposed to one born in a colony from slave parents).

Considering that this cannot be a valid meaning nowadays, I'd surmise that this is the name that non Jamaicans would use to designate Black Americans of Jamaicans origin as stated by the Partridge Dictionary of Slang.

According to The dictionary of Jamaican English, the Congo negroes were later arrivals than the Guinea negroes. The latter looked down on the former.

BTW the slur for Italian is derived from the term Guinea negro, via a stage where it was used for all darker-skinned peoples, then specialized to Italians.