Sounds like they were swimming around because they were hungry and going after the food. Whenever I feed my 40gal breeder tank full of CRS the whole take erupts in activity with the shrimp swimming around to try and find the food. When I feed Mosura Bioplus or another powdered food they often swim upside-down at the top and try and pick pieces of food off the surface.
If they swarm the food then it is a good idea to feed them. If they ignore it then you don't need to feed them.
If they swarm the food then it is a good idea to feed them. If they ignore it then you don't need to feed them.