Selective enforcement isn’t specific to racism — if you have a law which primarily impacts teenagers while other people break it with far lower penalty rates, that’s selective enforcement even if everyone is the same race.

This does commonly fall upon racial lines in countries like the United States with a long history of racial discrimination but it’s not exclusive and it’s important for anyone building systems to consider pitfalls like this because we know the users are likely to assume that a computer is unbiased.

Disproportionate impact is not the same thing as "selective enforcement". Selective enforcement means consciously choosing to enforce a law more commonly when a particular racial group breaks it. It does not members of a particular racial group disproportionately having the law enforced against them because they disproportionately exhibit a particular non-racial trait that is correlated with higher enforcement.