I read it as both children acting in bad faith. The hummer acts in bad faith by following the letter, not the spirit of the law and humming "loudly and triumph

I read it as both children acting in bad faith. The hummer acts in bad faith by following the letter, not the spirit of the law and humming "loudly and triumphantly" in as annoying a manner as possible. The hummee acts in bad faith by victim-playing — overstating the harm caused by the hummer and making a "dramatic display of suffering"