I agree with Fieos, save your bjj to your sparring partners. Using it on animals is just too risky. Unlike humans - animals have claws, they're very powerful, they could have rabies , and becomes really unpredictable when agitated.
Professionals come in a team of two or three just to diffuse a single black bear or a gorilla. And they use guns and tranquilizers just to put it down. No amount of bjj or muay thai skill can go up against an angry bear. A right hook from a bear can cause cerebral bleeding or worse lose your head.
That kid is very lucky to have even subdued that dog. I woulda run or chuck something at it if I was him.
A good sparring partner is the best way to practice your skills. If you don't have one, a good ground and pound bag or grappling dummy could be good especially if you wanna train at home.