It seems this plan wanted to avoid all of the RMD rules around the first RMD payable by April 1st following the Distribution Calendar Year or allowing active non-owners the opportunity to defer payments until severance from service. As Peter noted, the plan can provide for an involuntary distribution based on a reaching the plan's normal retirement age. I work with a 401(k) plan that requires lump sum distributions be made to the participant when the participant reaches age 65. Essentially, there are no RMDs payable from the plan due to reaching age 70-1/2, or 72, or 73, or 75, or any other age past age 65. The plan also pays lump sum death benefits which pretty much means no RMDs are paid from the plan.
Does this ESOP condition the payment based on the calendar year in which a participant reaches age 70-1/2 regardless of whether the participant is active or terminated? If yes, and the account is paid on the value of the stock appraisal (assuming it is not publicly traded) received in that year for the end of the prior year, there should be no problem making the payment timely during the year in which the participant reaches age 70-1/2.
If the ESOP is making payments using the RMD calculations as a minimum, then a payment made before the participant reaches the RMD age for a year will not be an RMD. It would be an eligible rollover distribution.