Rewatch the videos. Vandenberg didn't advocate rapid rudder inputs reversals.
It has to do with rudder crossover speed. It applies to light aircraft, airliners, fighters, etc. At high AOA the rudder can have more roll authority than the ailerons. Vandenberg said "if you're at high AOA and the plane isn't rolling with the ailerons, considering using some rudder. But as anyone who's done spin training will tell you that's also how to enter a spin. So be very careful using the rudder."
You can verify where it occurs in any aircraft. Put in large cross control inputs and check at which speed the plane won't roll. Lower AOA will reduce in rolling with the aileron input. Higher AOA will roll with the rudder input.
Panic isn't the right word. The A300 was the most sensitive rudder in the airline industry. That, and the sensitivity of the old style rudder limiters, wasn't well known prior to the crash. So a healthy rudder input by the startled FO resulted in a 'startle' reflex and he put in an oppposite rudder input, and that surprised him. Similar to a PIO and it went back a forth a couple more times before the vertical stabilizer failed due to loads above the design limit.