If that confirmation letter is accurate, it seems pretty clear that this was a 2018 distribution required to be reported on a 2018 Form 1099-R. It's obvious that the funds can't be contributed to the Roth account before they are distributed from the traditional account. However, the confirmation letter from the plan administrator may or may not be sufficient to satisfy the IRS that the distribution year or the Roth beginning year is 2018 if the distribution is reported on a 2019 Form 1099-R.
(The actual date for the beginning of the 5-year period for Roth account qualification purposes is January 1 of the year you first contributed to the Roth account, so stating it as December 28 is a bit misleading. Perhaps this is just another indication of the competence of the plan administrator.)
