But - total or percent? And overall or in its size range?
Put simply - a "city" of 10,000 that adds 1,000 people will be fast growing ( a 10% increase). But a "city" of 100 that adds 20 people would have a 20% increase, and a city 0f 2,000,000 that adds 5,000 would have a 500% higher absolute growth. So without defining growth further the claims to be fastest growing are meaningless.