Interview with one of the archaeologists researching the findings here.
Is it art?
"We've looked at all possibilities, but in the end we are really certain that this must have been made by an agent who did a very deliberate action with a very sharp implement,” says Joordens. Her team tried replicating the pattern on fresh and fossilized shells, “and that made us realize how difficult it really was”, she says. It sounds like you'd really need to apply pressure with a sharp tool. I was trying to think of natural process scenarios, but can't really.Close inspection under the microscope suggested that the engraving was intentional. The weathering patterns of the grooves, each of which is about 1 centimetre long, show signs of significant ageing, and there are no gaps between turns, indicating that the maker paid attention to detail. He or she probably made the engraving on a fresh shell, and the newly made etching would have resembled white lines on a dark canvas, Joordens’ team notes. Sand grains still embedded in the shell were dated to around 500,000 years ago.
The closest I could come up with is a small animal with evenly spaced claws swiping down once with enough force to create three-ish grooves (yet not break the shell), and then doing the same one more time randomly starting at the apex of what would looks like an inverted 'V'. Maybe a creature was trying to get at the food inside the shell? Not very likely but if I had to posit a 'natural' process I guess that would be it.