It sure happens, especially for the secondary people (family migrated because one person got a job). But I disagree with this as a generalisation. There's people who move explicitly to get to the new culture, those not connected to their home country, those just curious for something new, etc. I migrated multiple times now and I've seen lots of variety. You'll run into people from X who move specifically to the Xs neighbourhood, and people who resent X-specific meetings. It's really preferences and situations and many are shared/common but not something "natural".

Keep in mind that it's easier to see the number is Xs hanging out together in an Xs neighbourhood than how many random Xs are there individually in the city. (That you may not even realise where they come from)