That and the guards told him they have not seen the wagon or people either. And even if they had taken the wagon around, the guards would have seen them. May thoughts are the wagon never made it to town and was waylaid somewhere in between the two towns.
Of course once we leave town and head west Rodin will be looking for signs of a wagon leaving the road. So if they left the road and went around, he should spot that.
I figure that if he takes 10 in his survival check to spot the tracks that gives him a 15, which I hope will be enough to spot wagon tracks leaving the road since that is not a normal occurance. And if someone else is skilled at survival or tracking, then they can help him and boost it to a 17.