Nothing to worry about. The rollover of a qualified offset distribution is the same as a 60-day rollover except with an extended rollover deadline. The code M on the Form 1099-R will be sufficient for the IRS to understand that the rollover was permitted. Just be prepared to mention that to the IRS if they question the rollover, which is extremely unlikely. If fact, if the rollover actually did occur within 60-days of the date that the plan declared the offset distribution, it would qualify as a regular 60-day rollover.
Form 5498 is a form prepared by IRA custodians to provide the IRS with information regarding any deposited into an IRA (other than by nonreportable trustee-to-trustee transfer from another of the same type of IRA). The custodian properly reporting the rollover of the offset distribution in boxes 13 and not box 2 just provides additional confirmation to the IRS that the rollover was permitted beyond the regular 60-day deadline, matching up with the code M on the Form 1099-R.
