If the sled was rolled over it may have ice between the throttle lever and cable, click the throttle a number of times to clear the ice. If the machine is started with the throttle open it will go into limp mode.
If the throttle cable was rerouted or the handlebars changed etc he may have pinched the cable somewhere not allowing the throttle body to return to the idle position?
If he had the hood off did he put anything into the intake (rag) to keep stuff from falling in while he worked on the sled. Someone else did and did not take the rag out before reassembling the hood resulting in the rag getting sucked into the throttle body preventing it from returning to neutral? These are all SWAGS, so if nothing is obvious he may have to take it to the dealer.
