My wife is from Kenya. Here's the complete explanation: There is a Swahili that we learn in school and it’s how we should be talking and there is one that is not for education but just from the hoods. Mambo is another way of saying hi like we have different greatings in Swahili sanifu and Swahili slung. For example in Swahili sanifu you would say jambo Gaétan and the response will be sijambo. And in slung you would say mambo or niaje or sasa or even vipi and here the response will be poa
Salama means "peaceful" and it is usually the response to a question, like "How did you sleep?"
It is unfortunate that another Duolingo question in the Greetings lesson gives the translation of "salama" as "Hello". Report that if you see it! I think salama would seldom be used to initiate a greeting.
Perfectly acceptable, but that is when you greet someone with a question (equivalent to "How are things?") Maybe that is why it isn't accepted here as a translation for "Hello!"
But it's hard to illustrate without any context in a single sentence this common question-and-answer format (e.g. "Hujambo?" - "Sijambo!") for Swahili greetings, and they just don't translate directly to English greetings (e.g. "Hello!") that aren't expressed as a question.
That's an interesting thought. I read that too, although interestingly enough I have found some evidence that it's not the case. I don't live in Africa, but have many friends native to Rwanda and Tanzania who, when asked, have said that 'jambo' is a standard greeting for everyone, tourist or not.