Africa is the world's second largest and second most-populous continent, being behind Asia in both categories. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area and 20% of its land area. With 1.2 billion people as of 2016, it accounts for about 16% of the world's human population.
Thank you for the interesting question! I am not aware of any companions of the Prophet (S) who travelled all the way to Cape Verde, especially since most of the early Muslims did not have strong skills with boats. Perhaps this refers to someone else who went there (such as an explorer, trader, migrant, or general) who said something similar, or maybe it refers to someone who stood at a different location and said something similar.
However, absence of evidence is not proof that it did not happen. Possibly, someone will locate evidence that this happened!