Unknown family member

I was in Port Elizabeth South Africa, some friends who have a holiday home just outside the town invited me for a short stay. They organized a barbeque for friends and neighbours whilst I was there and I got chatting to one them, a woman a few years older than me. I started chatting about my fathers stay in Port Elizabeth during the war, he was a merchant seaman who escaped the fall of Singapore and had some adventures before landing up in PE. I also recounted the story of receiving boxes of sweets from South Africa during sugar rationing, a shoebox full would arrive every two months and dad insisted that I shared them with the other children in the street. I felt the atmosphere cool. Names were mentioned and it turned out that the sender of the sweets was the woman's mother, a strange coincidence, made even stranger when she told me she was my half sister. It turned out that the woman was very angry about the situation and left almost immediately and I have heard nothing since.