IANAL, but I believe the difference between Miles and Miller from a legal standpoint is that Miles knew what his friend was planning on doing with the gun, which makes him an accessory, while it seems Miller has argued that he didn't know anything about the situation and was just simply bringing Miller his "property" because he asked him to.
Now, I personally don't believe for a second that Miller didn't know that something was going down. Regardless, if I'm a head coach or school admin and you are handling and randomly bringing guns to people who are hanging outside a club, AND those actions lead to a woman being murdered, you are off the team immediately, charge or no charge. I think it's insane that he is still playing basketball for Alabama.