Replying to my own post because I spent a bit of time calling the IRS and Vanguard to find the answer.
Not everyone doing a mega backdoor Roth will run into this (because not all plans have the auto-conversion option), but some will, so FYI: One of the 1099-Rs, Distribution code G, was for the auto-conversions Vanguard did from the after-tax funds into the Roth 401K. The second 1099-R, Distribution code H, was for the rollover from the Roth 401K into the Roth IRA. The differing amount was, as suspected, the difference between initial contributions and growth before rollover.
I'll report both and the software will SAY I took $58,839 in total pension distributions, but ignore the wording - this is better thought of as total pensions activity, since the 28k was converted to the Roth 401K and then the 30K was rolled over into the IRA. Same money rolling around, but different events. If I hadn't done the rollover, I would have only gotten the G 1099-R (and still would have reported it).
None of it is taxable, the IRS isn't losing sleep over the $0.07 that accrued while Vanguard was performing the auto-conversions. But note, if your plan doesn't support Roth 401K auto-conversions like mine, your taxable growth will (hopefully) be much more than $0.07 and the IRS will most definitely care, so report that ish.
