My personal opinion on this, now that I have read both articles and rewatched the clip several times. I can only conclude that van der Merwe grossly overreacted. He most likely has a short temper and doesn't explore any probabilities beyond his own nose. Could there have been an attempt to steal the phone, yes, but assault is assault.
This didn’t happen on his property; this happened in a public space on private property within his own space.
Him being in the mind that the woman had stolen his property, given the circumstances, then he should have engaged civilly. He has shown zero tact other than aggression.
There not being CCTV coverage, he doesn't have a case.