your are both right...
you can take the whole plant and put it back under veg lighting conditions. (18-24 hours lights on.. I would go 24/0 for a re-veg)
You can also leave a few buds on the bottom of a harvested plant, trim back it's roots, and throw it under the above lighting.
Marijuana is a photo sensitive plant.. which means, that it will determine it's phase of life directly in relation to the amount of daylight hours it recieves.