"They seemed to think the 401k funds should count as income on my 2018 return and need a revised return."
It appears that TaxMama thought that the distribution from the 401(k) occurred in 2018 rather than in 2019 and that early in 2019 you received a 2018 Form 1099-R with code G in box 7 and $0 in box 2a. However, it's clear that the distribution you are asking about here occurred in 2019. As the trust company indicated, the Form 1099-R for this distribution from the 401(k) will be a 2019 Form 1099-R that you will receive near the end of January 2020 because the distribution occurred in 2019, and is reportable on your 2019 tax return. What you did with this money after it was distributed from the 401(k) has no effect on which year's tax return must show the distribution. Unless you made a distribution from the 401(k) in 2018, there is no 401(k) distribution to report on your 2018 tax return.
The "April 15th" deadline is for regular contributions to an IRA. The April 15 deadline has nothing to do with rollovers. If you made a regular contribution to a traditional IRA for 2018 but did not report it on your 2018 tax return, you need to amend your 2018 tax return to include it, but this has nothing to do with your 401(k) distribution.
I have no idea what payment of "interest" TaxMama is referring to. Nothing about this distribution and rollover involves any interest.
