He's actually sorta right, but not in the way he means.

California has been losing native-born Americans for decades, since at least the early 1990s (other than a 2-year blip before the dot-com boom). Yet they still gained population in the 90s, 00s, and through 2017 through massive foreign immigration.

Trump's visa and immigration policies substantially reduced foreign immigration. Biden was unable to reverse that before COVID killed immigration in 2020.

As a result, CA's population growth slowed in 2017, stalled in 2018 and 2019, and was negative in 2020 and 2021 directly due to decreased foreign immigration.

CA Net Domestic Migration
2021 -276,663
2020 -221,770
2019 -203,414
2018 -155,281
2017 -137,546
2016 -122,369
2015 -79,938
2014 -46,321
2013 -53,692
2012 -41,795
2011 -51,326
2010 -169,336
2009 -249,652
2008 -220,932
2007 -198,455
2006 -204,553
2005 -220,994
2004 -96,806
2003 -13,720
2002 -50,271
2001 -9,363
2000 115,505
1999 -78,848
1998 -69,874
1997 -89,128
1996 -152,100
1995 -255,435
1994 -382,545
1993 -428,455
1992 -393,533
1991 -210,800
1990 -147,991


CA Net International Migration
2021 27,424
2020 76,990
2019 74,028
2018 71,300
2017 112,814
2016 141,892
2015 156,870
2014 131,001
2013 116,528
2012 98,297
2011 99,179
2010 122,991
2009 160,510
2008 195,704
2007 174,266
2006 151,801
2005 137,728
2004 160,110
2003 160,234
2002 182,480
2001 223,612
2000 169,240
1999 246,911
1998 248,064
1997 258,387
1996 269,147
1995 227,554
1994 217,071
1993 243,302
1992 275,287
1991 262,362
1990 226,991

Note: CA continued to have more births than deaths throughout much of these years. So even if total migration (domestic+international) was negative, the state continued to have natural positive growth until 2019.