Jann is minding his own business. He is playing by himself in the courtyard with a wooden sword: this definitely constitutes minding his own business. Nothing that follows is his fault.
"I never said I wouldn't go in them," Milo points out, this being the crucial distinction as far as Milo is concerned. "It wouldn't be that hard to sneak in, I bet. And if I did it right when there was gonna be a new moon, I could just go outside when you were done petting me and nobody might even know."