I think a lot would depend on staging. Where is the wizard, where are the elementals? If the wizard and elementals are closer to the wagon it at least offers a clue as to the situation but if the soldiers are close and appear to be defending the carriage then I might feel railroaded.
Were there clues to the situation? Put some things in place that might give it away but not too obvious. A crest on the carriage that does not match the one worn by the soldiers perhaps.
Given opportunities to figure the situation out if I only looked would make me lean toward I made an error of assumption. If there are no clues then I might view it more as a despicable trick.
