Sometimes Visual Flight Rating is just not high enough standard in certain air space corridors.
People once thought prop wash was a disturbing phenomenon.
Cheap shot against VFR pilots....
There was a fully qualified CFI next to him that allowed a dangerous condition to foster after a warning from the tower and basic flying 101 rules of maintaining distance from large aircraft due to wake turbulence.
It's Visual Flight Rules (not Visual Flight Rating).
Even if both aircraft were on IFR flight plans there's nothing to prevent the same thing from happening. If the trailing pilot (the Cessna) in this case accepts a visual approach even while on an IFR flight plan then the pilot is responsible for separation including wake avoidance.
The CFI should have corrected the student's spacing in order to provide appropriate separation.
Chris - PP-ASEL (Instrument Student)