To be "out of touch with" a group of people means that you aren't paying attention to them and you don't understand them. But you wouldn't use this phrase to talk about a group of people from far away that you have never learned anything about. You use "out of touch" to describe not knowing a group of people that you're supposed to know well, or that you used to know well.

For example, you can be "out of touch with" teenagers or young people:

I'm not even 25 yet, but feel like I'm already out of touch with teenagers these days.

In addition to being "out of touch with" groups of people, you can also be "out of touch with" the ideas or culture that are associated with them. For example:

They accused Obama of being out of touch with the issues that ordinary citizens really care about.