You answer that it is All an RMD
and that the amount in box 1 is the RMD amount for that plan.
_______________________________________
This Question starts being asked once you reach age 73 for all 1099-R forms. Partly because there is nothing on the 1099-R that distinguishes a pension from a number of other 1099-R forms, where you-yourself have to calculate and initiate the RMD distribution every year.....like for a 401k plan.
Yeah, Defined benefits plans have an RMD, but that amount was pre-figured by the plan and automatically conforms to IRS distribution rules.
___________
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*