It is rude to ignore a greeting.
Hannah walks into work and sees Matt, who she doesn't know very well, working at his desk, so she says, hello.
Matt wants to react to Hannah.
Matt gives a big smile and says good morning to Hannah.
Matt looks up at Hannah, but quickly looks down, returning to his work.
Hannah feels that Matt seems like a nice guy and plans to talk with him in the future.
Hannah thinks Matt isn't very nice, and doesn't bother trying to talk with him anymore.