It's only very faintly familiar to me, Kenny ~ I can't think where I might have heard it, other than in a tv-documentary about South Africa in the 1930s (not that I watch many of those).
I suppose it's possible the performer was using it because it happens to rhyme with a much much stronger word ...
... which, coincidentally, I saw a feature about on British tv the other day, in which it was described as something like The Last Taboo Word, i.e. it takes a very brave performer to actually use it on the telly ... and he should be prepared not to work in tv for quite a while after doing so.
I agree with Ewie as to why munt was chosen. I doubt very much indeed that the performer realized what the word means (or meant) in southern Africa. I am certain it is not used in the UK in that sense. I've only heard the word once before: there is a "squat party" organization called "The Tribe of Munt" who organize illegal dance parties. I have a feeling they don't know either.
In English terms, to my knowledge, it came from the idea of getting 'munted'. I.e: taking loads of drugs to the point of getting annihilated.
Ergo: tribe of munt.
Further, the term could also be used to call someone ugly (munter). As if they were on too many drugs, and their face was contorted because of it.
Tbh, I haven't really heard any of these terms used this millennia, so whether the use of munt, munted, or munter have evolved in the last 20 years, I couldn't in all honesty say for sure.
Either way, I think this reply is 9 years overdue!