I would say that's not the key takeaway; it's about the relationship between income and children within a country.

From the conclusion:

"Past fertility research largely focused on understanding fertility decline over time and the negative cross-country relationship between income and fertility. The most important mechanism in explaining these patterns was the quantity-quality tradeoff. However, much has changed over the last few decades. In particular, fertility is no longer negatively related to income across high-income countries. Instead, family policy, cooperative fathers, favorable social norms, and flexible labor markets have become key determinants of fertility choice. Thus, a new era of fertility research has begun."