Your understanding is incorrect. Let me elaborate: Any Roth IRA contribution that appears on a 2022 Form 5498 is a contribution made for 2022, not 2021. A Roth IRA contribution made for 2021 can appear only on a 2021 Form 5498.
Refer to the instructions for Form 5498 Box 10: https://www.irs.gov/pub/irs-prior/i1099r--2022.pdf
The key is that the amount in box 10 of a 2022 Form 5498 represents contributions "designated for 2022."
