It could be what you say, but I’m not convinced that they are feeding so much as gulping for air air/water surface interface where the water is oxygenated. A possible reason why they are at the surface is that there are so many cats and smaller bait fish upon which they may be feeding that are concentrated in a big school. Their abundance may using up the oxygen below. The bait fish look like they could be gizzard shad or possibly white perch as they go by on their sides on the upstream side of the dock. They are possibly on their sides because of a dissolved oxygen grab or lack of space at the surface.
Also, it is at night so no D.O is being produced, but there are plenty of fish to use it up in a limited space. This happens with menhaden at times causing large kills. Cats aren’t exceptionally sensitive to low D. O. The other question that comes to mind is whether there is a warm discharge of some type just upstream from there, such as an industrial discharge, STP, or other that is attracting all of these fish in the first place.