Unfortunately, you’re correct. HAD this been labeled an “act of terror” by the Secretary of the Army, all military wounded or killed would be eligible.
Specifically:
a. The Purple Heart is awarded in the name of the President of the United States to any member of an Armed Force or any civilian national of the United States who, while serving under competent authority in any capacity with one of the U.S. Armed Services after 5 April 1917, has been wounded or killed, or who has died or may hereafter die after being wounded
(1) In any action against an enemy of the United States.
(2) In any action with an opposing armed force of a foreign country in which the Armed Forces of the United States are or have been engaged.
(3) While serving with friendly foreign forces engaged in an armed conflict against an opposing armed force in which the United States is not a belligerent party.
(4) As a result of an act of any such enemy of opposing armed forces.
(5) As the result of an act of any hostile foreign force.
(6) After 28 March 1973, as a result of an international terrorist attack against the United States or a foreign nation friendly to the United States, recognized as such an attack by the Secretary of the Army, or jointly by the Secretaries of the separate armed Services concerned if persons from more than one service are wounded in the attack.
So why wouldn’t Clause #6 apply to this incident? I seem to recall elements of evidence concerning Hasan’s communication with al-Qaeda operatives outside the US. If that can be proven, then the only thing holding back a Purple Heart determination is pure politics. Hasan being a member of the USArmy would have no bearing because his entry to service would be under the color of treason due to collusion with an international terror organization.