Does it matter who it was?
Why is it ok if it was the sister but not another woman?
Do you guys realize that if you're considering the gesture as inherently romantic or sexual in nature it would be weird if he did it to the sister?
But like it's not, it doesn't have to be
It doesn't really matter if it was the babysitter cause the gesture can just a polite way to like guide her out or something
A man touching a woman's waist doesn't have to be a big deal