Look at the planning, the timing, the training a guy would need, all the money he spent and the firepower he had. The machine gun is a big clue. Those are difficult to acquire.
No "snapping" snaps like this. Then reports by neighbors that he was gone for six months recently. Asian girlfriend, or friend.
A false claim of credit in Las Vegas will effectively shred the Islamic State’s news agency’s credibility. It will become a news agency that was once reliable, and now associates itself indiscriminately with heavily armed crazy people in casinos. I see little advantage in such a shift. When Amaq claims an attack, it makes itself hostage to the facts that are revealed in the follow-up investigation. The vast majority of the Islamic State’s claimed attacks were undertaken by men acting in its name, often after leaving short video statements confirming their intentions.
https://www.theatlantic.com/international/archive/2017/10/isis-amaq-las-vegas/541746/