"They are from Tanzania"
So "wametoka" should mean they have recently come, but I think I learned somewhere that it can also be used to indicate where they were born and/or grew up. In which case it is a correct translation of "They are from" and, in this example, they are Tanzanians.
However, when I look it up, everything points to "wanatoka" being used to identify people's origins in this way. See for example lesson 7b here (scroll to Question formation): https://www2.ku.edu/~kiswahili/pdfs/all.pdf#%5B%7B%22num%22%3A75%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22FitH%22%7D%2C796%5D
That would indicate that "Wametoka Tanzania" is an incorrect translation of "They are from Tanzania". Does anyone have a better source on this?