I believe you. If your friend is addicted, he's addicted, but it's not chemical. Some people also break open a bucket of ice cream when they get depressed, but ice cream isn't chemically addictive either.
What does it matter.
Let's say that I could prove that a gun is designed to kill but a knife is designed to spread butter. But if someone kills you with a butter knife, you're just as dead as if you were shot with a gun.
Besides that, how do you know that it's not chemical? Isn't it possible that some people could become chemically addicted to THC?
But it really doesn't matter to me because I think that people that take drugs are idiots. If you're never done it, you should try to ride with a cop on a Saturday night. Just about all their calls are drug related.