Having read his "Almost Human" book... these are not caves you casually enter. The passages to get to the Naledi burial chambers are impassable to adult males and most women, and are very deep and far in the cave system. He specifically recruited petite women with caving experience to work on his projects.

https://en.wikipedia.org/wiki/Rising_Star_Cave

"A portion of the cave, used by the excavation team en route to the Dinaledi Chamber, is called "Superman's Crawl" because most people can fit through only by holding one arm tightly against the body and extending the other above the head, in the manner of Superman in flight"

Or take a look at this map: https://www.ucl.ac.uk/human-evolution/sites/human_evolution/...

Plausible but

  The burials and drawings were made over a long period of time,