I got this off a .ke ___domain site that has an "African proverb of the day":
> In the 1970s Julius Nyerere (then the President of Tanzania) used this proverb in a speech at the United Nations in New York. The Democratic Republic of the Congo (then Zaire) Ambassador to Great Britain used this same proverb in a talk to a group of Missionaries of Africa (White Fathers) in London. The meaning was the same: In the Cold War between the (then) two great super powers — the United States and Russia — it was the poor Third World countries such as those in Africa who suffered and were victimized.
so that's probably why we've heard it; but it's probably much older than that. i didn't dig in to it too hard because that site was really slow, i got the attribution, though.
you'll note it has a slightly different connotation - the "reeds" aren't the citizens of the warring countries - the "grass" is Africans.
