It's entirely possible that the employer contribution made in 2025 was related to your participation in 2024 and was not a mistake. Ask this employer about it. Employer contributions are often not made until after the end of the year. They have until the due date of their tax return to make the contribution.
With regard to your taxes, the employer contribution is not reported to the IRS. Nothing about it would go on your 2025 tax return.
