No, all the signs do NOT point to him being homicidal. But they do point to him possibly being very frustrated with school. I see that all the time with kids with ADHD (my other CL role over here https://www.medhelp.org/forums/ADD---ADHD/show/175
You need to go to school and talk with his teachers and get their feedback. Does he have trouble concentrating? Does he lash out without thinking? Does he have trouble with homework? There are a lot of questions I could ask and a lot of information I can give. But you really need to start at school. And I would also talk to last years teacher.
By the way, it is not unusual for boys of this age (and older) to draw very graphic pictures of violence (like tanks shooting people, monsters, etc.) Putting that into video form is now the new thing. And he sounds like a fairly sharp kid to make his own video at his age! It also possible that he is just really bored with school. Having been involved as a teacher and principal for a ton of years, I have seen both types of kids - the bored, intelligent and the adhd intelligent kid. So ya, you really need to talk with his teachers. Please get back to me if you have any questions about any of this, or after you have talked with his teachers. Either here or on the adhd site. Good luck