The same thing happened to me once. I was on the rooftop and she waved at me and then i waved back. But it turned out she was just drying her hair. See these nepali girls go to the roof top with towel in hand and they shake their head vigourously sometimes looking like mild form of headbanging. In the process they just appear to be gesticulating.
 I was mortified and i also pretended to break dance. Anyways those were the pre hair dryer days.