How did the Scarlet Pimpernel fool Chauvelin in different events?

When Lady Blakeney reveals that the Scarlet Pimpernel will be in the supper room at a specifed time, he doesn't appear. The only person in the supper room is Percy, who is taking a nap on the couch. The Chauvelin is angry..... but not at this point suspicious. The Scarlet Pimpernel has effectively fooled him.