He is an American citizen who gave American secrets to a foreign power. That fits my definition of treason.
You may choose to disagree.
And the Constitution disagrees also: Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort. No Person shall be convicted of Treason unless on the Testimony of two Witnesses to the same overt Act, or on Confession in open Court.
Article III: Sec. 3