After a dinner party at a friends house I said on saying goodbye to someone I had just met that night, "I hope we do not meet again". I really did not realise I had said it, ok I did not particularily like the man but would never have imagined I would come out with such a remark. He went on to become a partner for a while of a dear friend, I was never invited to functions when he was present, I wonder why?
You say there's "no enmity" between him and his sister, overall. So unless there was a recent dustup or something, I'm gonna say it was probably just an error. If there's an issue, you'll know as time marches on.