yes, killing small creatures is in their nature. Especially with a Chowchow. They have high prey drives. And were bred as hunting dogs originally (but try telling that to the one that has taken up permanent residence on my parent's couch. lazy beast.
)
My concern is the fact that if he was able to get a bunny, he had to have been off leash. If it was at a dog park, that's cool, but most places (including regular parks) have leash laws and him being off leash can lead to tons of problems. He could chase a rabbit/squirrel into traffic and get hit. He could knock down someone else's kid and you'd get blamed (and a Chow injuring a kid is not going to look good, regardless of who is at fault. Law enforcement could seize him and put him down). You could be cited/fined for him being off leash. he could be attacked by another dog and injured (yeah, I know, he's a Chow, and they tend to come off better in a fight, but still) and once again- he's a Chow and people are so biased that even if he was attacked, he'll be blamed and you would be in trouble.
Don't mean to be horribly negative and all lecture-y but I adore my Chow and have dealt with the prejudice towards them for a long time. It's not pretty and I'd hate for something to happen to him or you because he was off leash.
Best of luck with him.
~Onyx