According to this article from Past Horizons, this art was discovered by Canadian archaeologists in the 60s and was simply “forgotten” until it was rediscovered in 2005.
The deposits covering the rock art, in part composed of wind-blown sediments, were dated at the Laboratory of Mineralogy and Petrology (Luminescence Research Group) of Ghent University (Belgium) using optically stimulated luminescence (OSL) dating. OSL dating can determine the time that has elapsed since the buried sediment grains were last exposed to sunlight. Using the constituent mineral grains of the sediment itself, it offers a direct means for establishing the time of sediment deposition and accumulation. This resulted in a minimum age of about 15 000 calendar years, providing the first solid evidence for the Pleistocene age of the rock art at Qurta and making it the oldest graphic activity ever recorded in Egypt and the whole of North Africa. The Qurta rock art is therefore more or less contemporaneous with European art from the last Ice Age, as known from such world-famous sites as the Lascaux and Altamira caves.