Just answer Yes it was an RMD and all of it was an RMD and you received all of your RMD for that one.
We have asked TTX numerous times to add a selection to indicate the payout was a regular pension payout...but they haven't so far.
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Technically, even your normal defined benefit pension payment is an RMD...you just have no control over it, and the "RMD" is calculated by the administrator of that pension and they send you whatever it is.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*