Retirement tax questions

Today we received a valid check (per Treasury Check Verification System) without any explanation of why.  In the memo field area is typed, in capital letters, "FLET FRESNO 12/2019 TAX REFUND 30 INT $ 29.51".   The amount of check is $2529.51.    

I filed 2019 tax return timely and already got a refund direct deposit to our bank account sometime around 2020's normal timeframe.   I also have filed 2020 Tax report and it was accepted March 17, 2021.  I'm expecting that refund in April 2021.

How do I find out why  I got this check?  I thought 2019 business was done. For years I have been pleased with TTax and hoping you can help on this.  I saw a similar post but some time ago. 

Thanks, in advance, for shedding any light on this situation.