This article (about the Assyrian-Syriac immigrants, who aren't as dark skinned as Somali, but are also hard hit) explains how they come into contact with a lot more sick people and thus transmit it:
Earlier this month, the country’s public health agency reported that people in Sweden with foreign backgrounds are disproportionately represented among those who need hospitalization.
That squares with the experience of Terez Kino, a resident of the city of Södertälje and member of its large population of Assyrian-Syriacs, an ethnic minority scattered across Turkey, Syria, and Iraq. She used to have five carers, all of immigrant background as well, who would come to her home and tend to her needs. Four are now sick at home with virus symptoms. Her elderly sister has also contracted the virus from her carers, and her brother recently died of the virus. Her son is now taking care of her.
https://www.csmonitor.com/World/Europe/2020/0427/With-scienc...
Lack of information in Swedish had very little to do with why Somalis contracted the virus. Tegnell even pointed this out.
This number seems high, but may be accurate for northen Stockholm (hard to check as only confirmed infections and deaths are tracked in available statistics). Certainly not for the whole of Sweden. Anyway, while the vitamin D deficency may be a part of it, many Somali immigrants live in apartments with a lot of family, often multiple generations.
So, social class is the main factor.
Also, one medical doctor of Somali decent in Stockholm said that it was hard to reach the Somalis with information on good prevention, as health info was at first only available in Swedish and the official minority languages plus English and Arabic. Information in Somali is available now.