I'm not an expert on this, but my understanding is was a trading pidgin language, made up between speakers of Arabic and various African languages and so forth. And then it got more systematised, and used for official purposes, and taught in schools, and now it's a first language for many of those who speak it. here is a site about swahili which looks quite interesting.

I suspect that for most European languages, it's more accurate to think of them as descended from pidgin latin rather than from Latin as spoken by people whose first language it was.