According to the Urban Dictionary "coconut" is slang for a person who's brown in the outside and white on the inside. Could this meme campaign be a preemptive attempt to shield against that slur? Real question.
It was around since before there was even a hint Biden was dropping out, and I've mostly heard it used in a complimentary, or at least lightly-ironic, manner, so I don't think it was made for that purpose.
That doesn't mean it can't serve that purpose, though.