The rock paintings at Avondzon, like some other places in the region, were painted by the bushmen, sometimes called San people,  hundreds of years ago. Many thin people of various sizes, wearing mostly black cloaks, together with animals, have been depicted in mainly red colors, in the shallow cave at the foot of the cliff.
The reason, why so many pictures have been made in just this cave on the estate, is not clear. Probably the cave was a sacred place and the paintings display religious rituals, important occasions or serve as a protection against evil spirits. 

Only in a few other places at Avondzon some small rock paintings have been found as well.
The presence of  the so called 'rain animals' as eland and hippopotamus like animals, one of which is even held by the tail by one of the figures, suggests the work of  medicine men or shamans as rainmakers in this dry area of the country.
In the center of the scene, a number of people are dancing with their arms 

thrust towards the sky and their knees bent. 

These attitudes are usually  associated with the trance dance.
Some others are crouching on the floor with their arms stretched backwards.

More information about the rock paintings in South Africa are found in the books:
"When animals were people" by  H.C. Woodhouse (1984)
"Images of power" by D. Lewis-Williams and T. Dowson (1989)