The voltage is not the real factor in the NEC rules for control wires in the same raceway or cable as the power wires. The Class of the power supply for the control wires is the major factor.
It appears the control wire for that ballast can be either Class 1 or Class 2. Class 1 conductors are permitted to be installed with the power conductors as long as they have insulation rated for the highest voltage that any of the associated conductors is carrying. In general Class 2 circuit conductors cannot be installed with power conductors.
"It is the first responsibility of every citizen to question authority." B Franklin