Conference goers are a great example population, since they are from everywhere and have no connection other than a shared interest in the conference proceedings, but the degree of trust among them is extremely (if recklessly) high.
Ethnicity, or "race," is a strong indicator of trust, since what is trust but a default line of credit you extend to someone with the belief that it will be reciprocated.
The U.S. has an american tribe, which includes anyone who seems american enough, and it can easily cross ethnic boundaries. A middle class black person, or an ethnic japanese person whose family has been in america for a few generations can become a part of a "white" trust network with only a few words in the right accent, with the right cultural references.
People trust each other based on their shared and demonstrated perceptions of power and authority. Belief in the same god is often enough, but barring that, alignment to the same institutions (rule of law, english "fair play," property, marriage, etc) will make someone initially trustworthy.
Here, being able to code gets you a long way because it has demonstrated a commitment to understanding, work, incremental success, among other things.
Someone who signals alignment to, or directly against those shared perceptions and institutions will make themselves untrustworthy. If you dress like a criminal, people will treat you like one. Similarly, if you dress like an oppressor, people will treat you like one.
There is nothing mysterious about trust. It only becomes complicated when untrustworthy people insist that they deserve your trust and that you are somehow deficient for declining to extend it.