All of your pension income is a "Required Minimum Distribution".
All retirement accounts, even pensions, must meet the RMD requirements.
However, the way pension plans meet the RMD requirements is by creating an annuity paid periodically (usually monthly).
Technically, any monthly pension payment is considered a Required Minimum Distribution (RMD) and the entire amount is an RMD. That is how you need to answer the questions. When asked "Was this withdrawal an RMD?", the answer is "Yes", then check "All of this distribution is an RMD."
(Be sure that the IRA /SEP/SIMPLE box is not checked in your data entry).
