Original sentence: Pitch angle is measured from the same reference line as angle of attack (conceptually the chord line), but to the horizon.Whereas, the angle of attack is measured from the (same) reference line to the direction of the arrival of the air to the aircraft/wing (caused by the relative motion between the aircraft/wing and the atmosphere)
Edited sentence: Pitch angle of an aircraft in flight is measured from the same reference line as angle of attack (the longitudinal axis of the aircraft), but to the horizon.Whereas, the angle of attack is measured from the (same) reference line, but to the direction of the arrival of the air to the aircraft