The gasses released as the flame is extinguished could be breaking the surface tension of the water behind the boat, the resulting influx of water pushes the boat forward.
This is how soap powered boats work.
Looks like a pop pop boat to me https://en.m.wikipedia.org/wiki/Pop_pop_boat
Yes it is http://www.thingiverse.com/thing:913528
@Daniel_Bull yep, a pop-pop boat was my first thought as well.
But when was the last time you saw a kid make one of those?
I have no small children, and no body of water to use this in. Yet, I still want to build a few. Maybe I need to find people with small kids to give them to.
@Winchell_Chung I never even knew they existed until I saw them at a modelling exhibition in Alexandra Palace and I was pretty amazed how cool they were 
I’m wondering if there’s a way to design one of these without the straws. You could just 3D print the tubes surely?
Am I the only one who’s first thought was “flame and plastic, what could go wrong?”
@Daniel_Bull when I was little, all the books of “projects for boys” had diagrams of how to make pop-pop boats out of scrap wood and copper tubing.
This is weird after only just seeing these made out of tin today! @Scott_Edy