So, Mr. Elliot would have claimed to be misunderstood if Anne had reacted negatively (instead of immediately turning her attention, giving no reaction whatsoever)? Or would he have still tried for a marriage with her, through other venues?

It is possible that he wanted both Elizabeth and Anne to think he was courting THEM, just as he is later shown to have paid some romantic attentions to Mrs. Clay. If he found them all receptive, he would choose the one that was the most to his advantage. Or am I assuming him to be too mercenary?