Wow! Well that just proves it! About as relevant as saying "Some children from the ghetto wind up graduating magna cum laude, so that proves ghettos are great places to raise children."
The statement was that anyone who send their kids to public schools is a total loser. A single counterexample is sufficient to counter a general rule.
In fact, in this city, the public schools are educationally superior, in terms of facilities, course offerings and quality of teachers, to the two private religious school, which are small and attract students almost entirely for religious and not educational reasons.