For the most part, you were told wrong, but I'm weary of this fight for the time being. You can search the archives for many discussions about this.
Kettlebells are kettle-shaped dumbbells that allow you to do certain ballistic power exercises, mostly involving an upward motion. They're a big fad right now in martial arts circles, and a couple of gurus are making a bunch of money off of the bells and books.
The long and the short of it is that there isn't much in kettlebells that you can't get from the Olympic lifts and variants. Kettlebells are expensive and hard to find, while barbells are everywhere. As far as a resistance program consisting of all kettlebell power movements, I don't think much of it. General training in basic compound movements to develop strength, mass, movement integrity, and injury prevention is more important than the development of power-oriented motor qualities. Aikido isn't often done with that kind of speed and power in practice... you'd run out of ukes. Ukemi involves some similar qualities, but seems to be good conditioning unto itself.