This is a mountain being made out of a mole hill. What we have is evidence that a series of hash marks were made for no reason we can see. Therefore, it must be symbolic. I'm not buying it, even if they are selling.
First, we have to remember that the Neanderthals did not much change their tool set for something like 260,000 years. If you find a Mousterian tool set anywhere you have Neanderthals. That is weird in it's self. Think about it, for 2600 centuries everywhere from Afghanistan to Gibraltar all Neanderthals used the same set of technologies. Not a lot of original thinking going on there. This has all sorts of problems, like where did they all learn the same tool set? Where did that knowledge come from and why didn't it change?
Second, the hash marks are not associated with anything else, nor is it reported that they are repeated anywhere else. One set, one place, once. Walk into a cave, find Mousterian tools, you have Neanderthal. Walk into a cave and it's painted like a '70s Brooklyn subway car, and everything else had been doodled on, the tools set is one of dozens locally, and you have humans.
Third, the definition of art is off. Art may not serve a practical purpose, but does do something specific. The Soluterian culture, which was modern human and followed the Mousterian, would make flint blades several time larger then normal and so thin and delicate that the could never be used as a blade. They are being used as symbols. They are art. What was found is not understood and drawing conclusions is not warranted.