In my own experience living in other countries and knowing quite a lot of other immigrants (as people tend to more easily bond with those living similar experiences, with the result that immigrants tend to mix more with other immigrants - and not just people from the same country of origin but immigrants in general - than with the locals), people who go live in other countries out of their own choice tend to have two main kinds of drives for that and hence personalities:

• People who moved elsewhere because they actually like meeting other people from different cultures and living life in different ways than the one they grew up in, or as you said "seek out other cultures".
• People who moved elsewhere driven by wanting to make more money and have a better life.

From what I've seen in a couple of countries, the former are a lot rarer than the latter, they're also generally more open-minded people. However the latter are not at all open-minded and in my own experience are often very conservative types, possibly even more so than the locals (this is my experience both with most of my countrymen when I was an immigrant abroad and with immigrants living in my own homeland).

Anyways, what you say about you experience with South Africans in the US does match my experience with South Africans in Europe, my point is just that your broader conclusion about openness of immigrants in general does not at all match my own - most immigrants out there are of the second kind and thus they're not at all more open minded than people in general and might even be more close minded (as I said, seen it both with my countrymen whilst living abroad and with immigrants in my homeland - and it seems to me that most immigrants are more conservative and less open minded than average, which is probably what leads some immigrants to form single-nationality communities when living abroad whilst in my experience the "seek out other cultures" kind tends to live amongst the locals).