It happened with Dutch immigrants in my family. Some came in the early 19th century, others in the 20th century, but they all stayed in communities with other people of Dutch origin and kept marrying other people from the same community for many generations. There are little towns in Wisconsin where the street signs are still in Dutch as well as English.

They know they're not Dutch the same way as actual Dutch people n the Netherlands, but their heritage is still important to them. I think some Europeans misunderstand how many Americans think about identity and think they're saying they're literally just as Russian/Swedish/Irish as someone who was actually born and raised in those countries, but that's not what most Americans mean when they say that. As a country where literally everyone but Native Americans comes from an immigrant background, people just aren't going to think about identity the same way as in other countries.