I don't think I fully understand your question. Generally, something is strange when it differs from the norm in some way. When you're introduced to a group of people who look radically different from any group of people that you know, you're going to think that they look strange whether you like it or not. There's not really any reasoning that plays into it.

Well they would be strange because by large the majority of people hardly travelled. Sure you had traders and explorers with the average Eastern European would most likely never left their village except for perhaps a market in a nearby town.

You didn't intermarry with other regions, you didn't travel, visitors were extremely rare. How could you possibly comprehend there other people out there?