wintering catfish

I have a question on wintering catfish.
We all know that flatheads are found in the hole in a dormant state during the winter months but do you guys think that they stay dormant for the whole winter or do you think that they have active periods when they go shallower to feed?
The reason I ask is I watched a gentleman last winter fishing in about 10-15 feet of water bottom fishing a shiner and he was slamming flatties. I must have watched him catch 4 or 5 of them in about an hour. These fish were definitely biting. He had the no rolls and his clicker was buzzing just like in the summer.
Do you think this was abnormal behavior or just a “they gotta eat”type thing?