This is as true in real life as it is in manga.
Don't expect boys to understand what a dropped handkerchief means unless you live in the 1800s and it's a universally understood etiquette.
Her way of teasing him deeply backfired this time. Well, despite of what he heard from her when those boys showed up at the bridge he still also thinks of her as a prostitute and nothing more. She still keep the facade too so this might take a while to clear out at this rate.