The way I have seen reactive squats described and the way I have done them involves a short free fall where your feet come off the ground slightly and you drop. Then you make contact with the floor and reverse the weight as fast as possible. The drop could vary from a few inches to catching the weight at a near parallel position.
It took me some practice just to work up to using any sort of real weight. You should try it first without a bar. Try to lift your feet up and let your body drop to near parallel position and then quickly reverse.
For speed squats it is much more controlled as you maintain tension the whole time and your feet do not move. Also you can't lower as fast as you can drop.