In your opinion what is the base for behavior like this?
could be, they were not Polish.Havok
in your profile, it states : Yes, somewhat
when asked if you know Polish language and I'm convinced you probably missunderstood the peoples language.
There are other similarly sounding languages to Polish, like Slovak language ( from Slovakia) or Ukrainian (from Ukraine) .
There are no reasons why would Polish people not want to be recognised as a Polish citizens unless they were some kind of weirdos or otherwise they were scared of you (maybe you tried too hard to get to know them).
Some other reasons could be, Polish people are very reserved towards unknown person . That's our Polish culture, we need time to get to know people before we can trust them or engage in conversation.
We are very formal to unkown person. I mean Poles living in Poland, because Poles from around the world are much different and more approachable- you should remember that.