Could this just have been fuel venting from the tank vent system - just as it is designed to do when the cold fuel warms up?
After all, your average non-aviator eyewitness is a pretty unreliable source of info in these cases. Any kind of vapour is usually "smoke".
As for "won't get back on the aeroplane" - it's funny how the same people will get back in their cars after they have been fixed!