Simple observation of the data also supports this conclusion. But our usual methods for estimating the NAIRU don't tell us why that happened. They are statistical methods, so they are simply not designed to explain changes in the NAIRU, only to identify those movements.
We must instead seek to understand the causes by using other information about the labour market, such as the composition of unemployment. One way to think about this question is to think of the NAIRU as capturing the types of unemployment that would remain, even when there is no spare capacity in the labour market and inflation is sustainably at target.