Maybe I'm missing something, but I'm genuinely not sure how the comment you replied to is implying that? I read it as saying the US woman should have adjusted her behavior.
It's more that the comment is missing the point of the grandparent.
Having worked across a lot of cultures, it's easy to spot how ignorant it is. And ignorance is fine but the poster is trying to decide how people Should Have Acted when they're clearly not in a place to really know that.
I've worked across a lot of cultures too. If you believe it's normal part of "Hindu" culture to put your hand on co-worker's knees, to the point that they are avoiding you, then I'm afraid you don't know as much as you think you do.
And I've been here quite a while!
Americans having to adjust to other people's cultures. Imagine that.