I glanced at that article, but I don't know where they got those numbers. According to the Census Bureau, the population of California has only dropped about 500k since 2020 (~1.2%) with just over 110k leaving between July 2021-July 2022.

But since congressional seats are done on a yearly basis, but on a per-census basis, it is useful to look at the comparison between censuses. From 2010 - 2020, California increased by 2.3 million people.