A question about the Dogon people of Mali and their knowledge of Sirius B?

The evidence that the Dogon people knew of Sirius B dates from around 1860, and consists of the first European anthropological reports about them. Since Sirius B was discovered in the 1840s, and was big, big news, all you need to explain this phenomenon is that the Dogon people were not totally isolated. If news could have reached them, they would have been interested and remembered, because they had, as a culture, always been interested in Sirius (the brightest star in the sky).