This is quite an interesting op actually.
My mother's family are Polish. They came to Britain during the second world war; they were part of the "first Polish diaspora" in this country.
Since EU enlargement and Polish migrants started coming to the UK in significant numbers, there have been quite a few conversations in my family about how different the modern Polish manner is compared to the old Polish mentality of the pre-war period that was then passed down to second and third generation Poles in Britain.
My grandfather, who was a decorated Polish war veteran, believed that the experience of the second world war and Communism, along with the massacre of the backbone of the pre-war Polish establishment, deeply scarred the Polish people and fundamentally destroyed their culture, which was really quite formal and put a lot of emphasis on manners and being polite and honorable -- and was, in a sense, quite Oriental.
Apparently, the way modern Polish people speak and use the Polish language is very different to pre-war Poland -- to the extent that it came across as being abrupt and rude to older Polish members of my family.
So I would suggest that there may be something in what the op's mother is saying, but it is not because Poles are innately rude but more that the Polish people have been brutalised over the course of twentieth century history.