Federal and CA State 2023 tax refund

I filed my turbotax Fed and CA state taxes several weeks ago.  My wife and I are retired and filed as seniors non-itemized.  Turbotax calculated we would receive $1,600 back from the Feds and would owe Calif $1,700.  We received our $1,600 refund from the Feds and paid the $1,700 owed to the Calilf FTB.   Last week we received a $30 refund check from the Calif FTB as a refund with no explanation.   Today we received an $850 check from the IRS as a tax refund.  While we are glad to receive the unexpected money, can anyone explain why this would have happened.  Was turbotax calculations wrong or what?