I dont know basically... after reading your thread, I was confused on what to say.
What kind of moral guidance would it actually be to say 'leave it' or even 'hold it'! Its meaningless... if she intends something else, or feels undecided already.
There are Polish girls with boyfriends in Poland, who struggle to reach UK, and when they do, their attitude is not similar usually. They would prefer something else.
Maybe she is considering UK... and leaving Poland behind. I knew a friend of mine, whose girlfriend went UK and then just became someone who was 100% different from what he knew. Its all about opportunities sometimes... love comes way at last, or often doesnt arrive at all.
So anything can happen in your case... he socialised with you very easy... you have no reason to not believe that she can be with you! Infact, I think you have more reasons to believe that.
Its definately not rare at all. Specially with those who hol themselves and only their singular selves first.