Zulu to English Other Linguistics Textbook Zulu

Hi
From "Teach Yourself Zulu".
Ukwanda kwaliwa ngumthakathi.
A literal translation is given: "Increase [of people] is refused by a wizard."
Please may I have an idiomatic translation, i.e. one that will be easily understood by an English speaker?
Is it really used to express thanks? If so, please explain how such a seemingly unlikely idiom can also be used in this way.
Best
Simon