Updated video footage from the robbery attempted posted a few days ago that captures what happened ahead of the vehicle. BBC did a major article on the robberies in South Africa with some background on them:
The gangs, according to Yusuf Abramjee, an anti-crime activist, range in size from about 10 to 20 members, and are just as confident in conducting a broad daylight strike in the cities as they are out in the countryside.
And when they strike, they are well prepared: AK47s, other assault rifles and commercial-grade explosives – allowing them to blow the back of a van off, and then walk away with the money.
Details here.