He may not want to march at the front of the army, but he certainly wants everyone around him to know he was behind it. Practically every word that comes out of his mouth demonstrates the lie in his words about Sammael. This is the same man who turned to the Shadow because someone else got all the credit he felt he deserved. It's in the FS nature to deride characteristics in others that they also possess! Demandred is every bit the glory hound that Sammael is, he just doesn't want to put himself in danger to be in the spot light. As he essentially says during the Cleansing.