You may want to just see if it happens again. This has happened to a couple of people before. Holding the accelerator pedal to the floor while cranking the engine seems to solve it on the rare occasions that it happens.
Even though the car is under warranty, they may not look at it for free...especially if they can't duplicate the condition. I'd hate to see you drop $100 just to have the service manager tell you they couldn't find anything wrong.
View my fuel log 2015 Mirage ES 1.2 manual: 52.2 mpg (US) ... 22.2 km/L ... 4.5 L/100 km ... 62.6 mpg (Imp)