[Jay O'Donnell]

POSSESS: (for a ROBOT) to carry (move while supporting BALLS in or on the ROBOT), herd (repeated pushing or bumping), launch (impel BALLS to a desired location or direction via a MECHANISM in motion relative to the ROBOT), or trap (overt isolation or holding one or more BALLS against a FIELD element or ROBOT in an attempt to shield them) a BALL.

According to this definition of possess from the manual, it should've been counted as an assist, since they "launched" the ball, based on the definition of launch.