Why aren't they friendly?

I was teaching English 2 days ago and one of my students asked me why it was that sometimes foreign (western) tourists are unfriendly and don't want to talk to them. This man in his 50's asked, "Do they want to 'protect' themselves?" I thought about Thai culture, how open they are with strangers about their own lives, and tried to quickly formulate an answer, "They don't understand the Thai culture and they don't know you, so they are afraid you might want to do something bad to them." American idioms flowed through my brain..."Don't talk to strangers." "It's none of your business." How could they possibly understand these strange and apparently unfriendly ideas?
I see sometime in the future I will have to teach them the word "privacy" and how it is so highly valued in western countries. Here it is not valued or understood. Perhaps it is the luxury of the rich, but not part of the thinking of the everyday person. Thailand is a community-based society, something we westerners have left behind us, to our loss I believe. These past years have been so stretching for our family, trying to learn how to live openly and be accomodating in this very different culture. As time goes on it becomes easier, how else could we live now with our open front garage door livingroom? Perhaps for the gregarious sort the adjustments would be easier, but we are of the quiet sort. We have learned so much these past years, and our lives are often enriched for it.