Or he may have found getting cozy with neighbors triggers his PTSD, if he has it. Look, I’ve worked with Somali and second generation Hmong refugees, as well as a lot of other immigrants. The answer to your question could be he is mistrustful of strangers due to getting burned in the past. Maybe he is shy? Maybe he’s just like a lot of Americans who think good fences make for the best neighbors. My husband and I have lived in the same apartment complex for ten years, and we don’t know any of our neighbors.
In psychology, there is something called the fundamental attribution error, wherein we attribute the behavior of others to their personal failings, rather than in their environmental context. This all sounded like a variation on that. Speculation tends to be riddled with stereotypes, assumptions, and “othering.” Either way, here’s hoping he feels trusting, safe, and comfortable enough, so he opens up. Keep trying and kindness is likely to win out.