That's not entirely true. Nick ran and found his mother and told her what happened and they, along with Travis, went to look for the body and found none at first...until it appeared in the tunnel. There's no indication to suggest that he turned "right away." After the shooting, Nick turned over the body and found that his friend was in fact dead. He hadn't turned.
Jenner very clearly stated that when a person turns depends on any number of things: some turn within minutes, others hours. We know from TWD, a person can be infected by a bite, or an airborne like virus (if it kills them), coming into contact with an infected person's blood or fluids (drinking or washing from the same water), or being killed by other means if the head is untouched - people that hang themselves turn - those that die by head trauma, do not.
Laura
