If you finsih the quote that comes next it ends with

"He said it, she knew, to be contradicted. His bright proud eye spoke the happy conviction that he was nice; and Anne Elliot was not out of his thoughts, when......."
Anne Elliot is never out of his thoughts. So much of his conversation with Louisa on the Winthrop walk was in reference to Anne. I think he liked the girls and enjoyed their company very much but although it was hard to tell which of the girls he was most interested in he did not turn a hair when he learned that Henrietta was spoken for. His thoughtless flirting with her could have ruined her chances with Charles Hayter. He just moved on to single out Louisa. Although he would not want to be with Anne, Mary certainly was there willing and able to be distinguished as a proper buffer to a man who had not made up his mind. And of course the very next thing he does at the end of the walk is put Anne in the Croft Gig showing that he was very aware of her all the time he was chatting up Louisa so particularly while Anne trailed along at the back of the group.