Just a theory here, but quite possibly a very intense "gustnado." Expected dry plains environment of S. Africa could also explain the abundance of dust.
Cu looks pretty high-based, and no real heavy precip core that I can see. Perhaps, could this resemble some of the gustnadoes or landspout-type events we see in eastern Colorado / west TX panhandle (high plains)? Throw in a freshly-tilled field or the tyical terrain down there, and you'd certainly get enough dust kicked up.
Just a thought anyway.