Bring any nuance to a charged topic and the ones who think in black and white terms will come to misinterpret what you said in the least charitable way.

equating skin colour with culture

Not equating. They said that people of an ethnicity are often also of a culture common among those of that ethnicity.

I'm in Costa Rica, and people are likely to (correctly) assume that I'm a foreigner here because I'm white.

It's not equating. It is, however, a way to tell what is likely.