The 1040 deadline was extended last year. Not the Q1 2021 estimated tax payment date. So if that extension payment was made on 5/15/21 last year, the resulting overpayment to 2021 was effective 5/15/21 (or whatever last year's due date was. I have trouble remembering.) That makes the Q1 2021 estimate late.

Now if they were in Texas, or whatever other places got until June 15 that doesn't apply.

And for $7 it is not worth spending time on. @BobKamman would probably tell you to suppress it.