Well, I do feed them on that side, so that is a possibility that they are just scavenging for their crumbs.
Although the driftwood is new, I noticed this behavior before I put the driftwood in. Infact, I put the driftwood in there because I was hopeing a fish or two would claim parts of it as their territory.
When I sit and watch them, I'll notice a cory go over to the left side every once in a while... I've heard cories fart on occasion