Seems like journalists failed to do their due dilligence on this one. From an international law standpoint South Africa has absolutely no obligation to arrest Putin as he would be protected under diplomatic immunity as stipulated on the Vienna Convention of 1969 (and custom). In fact Article 98 of the ICC treaty directly prevents this from happening.
What South Africa doesn’t want is the shit show of having Putin on an official visit. The guy will be bad PR and a liability to them at this point.
Compared to most constitutions on the planet, it’s considered a short one.