Cultures that dislike diversity are pretty low-trust. Russia, North Korea, Iran come to mind. White American conservatives don't trust anyone who isn't also them. And so on.
I think the user you replied to is referring to things like the Putnam findings on the effects of diversity https://drive.google.com/file/d/1FvFN8ACY6taivkcbzDGgYy1-EPb...
There are also cultures that aren't very diverse that are pretty high-trust: Denmark, Sweden, Norway, Japan, even China.
Which goes to say, diversity likely has very little to do with whether a society is low-trust or high-trust. It's more about politics and policy.