Yes, I believe the suspect in the Nice attacks was affiliated with a terrorist organization. One person causing mayhem couldn't have escalated that quickly and a terrorist group would be the most likely choice for causing that much mayhem and hate. It is their ultimate goal so it was most likely.
I believe the suspect in the Nice attacks was affiliated with a terrorist group because of the bold actions and amount of artillery that was used during the attack. It appears that most are willing to be affiliated by a terrorist organization and do massive attacks on innocent people. We can only assume by the actions that he is related to a terrorists group.
This was from what has been reported a very angry individual who may have had mental health issues. He was separated from his wife and children and may have felt he wanted revenge in whatever way he could. Isis only took responsibility today and at present there is only sketchy information given. He appeared to have a personality disorder, violent and in trouble with the police and no friends. I am sure his ex wife will be able to give a clear picture of this individual and it will be interesting to know what the trigger was for his actions.
The suspect in the Nice attack was most likely acting on his own, a lone wolf. This suspect might have pledged allegiance to some terrorist organization; however, he probably was not directed to carry out this attack by any group. Some terrorist groups have called for lone-wolf attacks, so it is possible that the suspect was inspired by someone else.
I do think the suspect in Nice was a "lone wolf" type of terrorist, not one who was trained by an organization. However, part of ISIS's M.O. is to encourage this type of attacks by unaffiliated people. So there's a good chance the terrorist actually was influenced by ISIS propaganda.