She believes him, inasmuch as she ever believes anything he says. He believes what he's saying--that much is obvious. He's wrong, of course, but try convincing Byerly Vorrutyer that he's wrong.

I don't want to argue with him. This is a party.

"Think that if you want," she says lightly, shrugging like it's no big deal. Which it isn't, if he's this determined to be a coward for the rest of his life. What's one conversation at a party while he slips in and out of fake drunkenness? Turning to escape the conversation, she adds, "Thanks for the spice cake."