I beg to differ.
If you're resisting arrest and armed, expect a cop to take pre-emptive action.
By the way, reports say he threatened someone with a gun as well, not just selling CDs. But that's beside the point.
Carrying a firearm is not against the law in the US*, although many crimes committed while carrying a firearm has increased penalties. But unless he was assaulting the police officers or otherwise threatening them I can't see why they shot him unless they are incompetent. It's not common, even in the US, to shoot someone during the arrest process.
*It is in some specific instances, as is how you carry a firearm