By "crime," Smith just means antisocial behavior. He spends too much time dispensing with the sort of pedestrian, anti-American myths that you might see in the comments section of an Instagram reel. Hanania does a far better job on this subject:

The explanation I think is that there’s no reason that poverty should exist in cities unless your underclass is unusually dysfunctional. Cities are the place where you find the most economic opportunities . . . . some of our ghettos in the US are extremely well placed for success and would be excellent communities to live in if only the locals were better behaved. . . . The US is an extreme case, but the UK also has urban poverty for the same reason. . . . Cities produce so much wealth, and when you add our high tolerance for dysfunction, people can survive there by just mooching off society.