You misunderstand their point. Assuming everything they said is accurate, the fact that the average tax is 2K is because those who would have been taxed higher already moved and were thus excluded from the tax.

With that being said I'm skeptical the average tax was 2K, because even a handful of ultrawealthy who stay would really distort the average. My guess is that they meant "most families would paid the tax paid only 2K"