It's the only way we can be empirically sure.
This paper plane seems to fly in a circle indefinately with the help of hot air generated via the stove. Theoretically it is possible and of course there are real-world examples of the use of thermals. However, as amusing/amazing this video is, I can't help thinking of easier methods to create this scene- a fine piece of thread +/- editing.
Would the thermals from the hot stove be adequate for a paper plane of those dimensions to generate lift? Are the ailerons realistically allowing the plane to stably bank in that fashion? Any skeptics/illusionists/aeronautical engineers/physicists/maths savants want to figure this out? ;)