I say its a flathead. the barbels look like they are maneuverable where as on a bullhead, the top 2 barbels stick straight up and don't look like there are any muscles attached to move them.
Also another thing is the coloration. The coloration of this fish is similar to the juvinile coloring of a bullhead. If it's that big nad still has that coloration, then its one really rare bullhead or just a flathead.
More proof would be the position of the eyes on its head