A misconception I think many people hold: "their culture here is so different, we could never be friends."
That belief alone has already prevented the friendship.
Have you actually tried?
Have you spent time with them before concluding you are incompatible?
Have you opened up, talked about love, about your family, the way you would with your Vietnamese friends?
If you do open up, yes, their background is different. They were born into a different family in a different country, so there are differences. But broadly, they understand you perfectly well.
On the word "Tây"
This next part is slightly contentious, but I find the Vietnamese word Tây carries a sense of othering. So I tend to say local people, or people here in Britain.
Because if someone of Indian heritage has lived here for decades, or was born here, is that person Tây? What would you call them?
The moment you divide the world into "them" and "us", the label itself has created a distance between you, when in fact we are very alike.
One specific misconception
In Vietnam we were often told that society over there is cold, that parents and children are not close.
That is not true. Living here, you see parents funding their children's university, children living at home.
The difference is that here there is a student loan system and at home there is not. So many families choose to let the child borrow, because it works out better for them long term. That is a financial decision, not coldness.