I’m not sure that anyone was capable of that. But being that the 11 yo had the mind of a 4 yo, that opens him up to suspicion.
Kids hear all kinds of weird stuff at a young age. Shoot I remember 2nd grade boys trying to be gross singing a little ditty "Suffocation" to the tune of "Alouette." "Pull a bag over your head, go to bed and wake up dead"... in that vein. (There were others about shooting the teacher, etc. But funny, nobody actually did it.)