I'm pretty sure Howells did know; it seems pretty clear to me that he's doing this on purpose, that he's portraying this state where a person gets locked into an emotion even though everyone else can see and possibly even the person themself sort of knows that the emotional is unreasonable. It's clear to the reader that Florida really does not have any romantic feelings for Don Ippolito, and Ferris just happened to eavesdrop on exactly the wrong part of their conversation.