Your neighbor is crazy...another reason to send your daughter to BS!
I would hope that it has no role at all in a decision whether to "send" a kid to BS. That takes the view in which BS is a bubble or a shelter from the world and reality. That may be a reason to limit interaction with the neighbor but I wouldn't let that sort of thing weigh on whether boarding school makes good sense for a child, even if it's far down the list of pros and cons.
But, yeah, the neighbor is crazy -- or not well-traveled. And if the observation was repeated and not just a one-off remark buried within a different train of thought, I think it falls somewhere closer to the "open hostility" end of the spectrum than the "blind insensitivity" end.