Headscarf not allowed as mask as it can fall off?

My wife was refused entry at the Cape Town Nike Factory Store Access Park, because she had a head scarf which was also covering her face, only her eyes were exposed. The security guard who was wearing a snood said she needs to wear a mask, a scarf is not allowed, irrespective of the material. The scarf worn was of a thicker material than his snood and was wrapped twice and pinned. The manager advised that it was a policy they instated because scarfs fall off..unlike masks or snoods? I explained that the scarf was thicker and more secure than even a mask or the snood that was accepted at the store. He only offered a mask and could not provide a valid reason why such a policy was instated. We felt discriminated against as there was no health and safety risk to instate a policy to specifically disallow head scarfs from covering the nose and mouth. I'd like to know what this policy entails and why it has been instated.