MOC must have had two Cadet spots available to him/her at USAFA this cycle. This creates the ability for that MOC to have two slates for that cycle. Each MOC can have 5 persons attending a DOD SA (charged to that MOC) at any given time. When a Cadet separates the USAFA for any reason, it creates open spot for that particular MOC.
Quote from Congressional Research Paper:
"Typically, one appointment per DOD academy per Senator and Representative is availableannually. In some years, however, a congressional office might have the opportunity to make nominations to fill multiple vacancies at an academy. "
Footnote 13: "Nominations are attached to a particular vacancy, so if a congressional office has multiple appointments available to an academy in a given year, a set of nominations is submitted for each vacancy." In the above case, the MOC is using Principle Nominations so he/she has two Principles for this cycle at USAFA.
Just thank the MOC staff and move on....all this is not in your control. Let the system work. Congratulations to DS and his friend.