I really don't think the Cessna was in formation with anything or that the two banner towing aircraft were other than coincidentally operating in the same area although they probably were aware of each other, certainly the Cub seems to be aware of the presence of the Husky. But it looks to me like the Cessna just happened to be flying in the same area, spotted the Cub but not the Husky and chose to pass close to have a look. With the Cessna pilot's, and his passengers', attention out to the right he clearly was unaware of the Husky but had he overtaken the Cub properly then this particular incident would not have occurred.
Had the Cub and the Husky been part of a banner towing team I would expect them to have radio contact so that the Cub might have been able to warn the Husky of the impending midair.
Had the Cessna and the Cub been flying a photo shoot surely they would have had radio contact so that a verbal warning could have been given. Furthermore, if on a photo shoot the Cub would have been the 'lead' and, since he was clearly aware of the Husky, would have had a duty to lead his flight out of danger.