Innappropiate joke?

The scene where Austin is looking for Cinderella at school with his two male friends, they do a Bachelorette Search featuring a lot of girls.

The female teacher stops it and tells everyone to go to class. Before she leaves, she waves excitedly at Austin's friend Brad and says "Hi Brad!" Brad waves, looking scared (embarassed?).

Is this supposed to be an innappropiate joke about the teacher and student having an affair? Or the teacher just liked Brad, a situation that can still be innappropiate?