White smoke is probably caused by unburnt fuel in the situation you're describing. It could be coolant, but my gut tells me it's not.
Next time you're out, try motoring for a little longer and at higher RPM's to see if you can duplicate the problem. It could be as simple as an issue with the injectors. There are more serious problems that can cause white smoke, but the serious problems usually lead to persistent smoke.
I would bet the motor just had a minor hiccup when the throttle poured on - maybe a timing issue? - and some unburnt fuel appeared as white smoke.
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