They give their hypothesis in the paper, and each is shown with a p value < 0.05, so is statistically significant (and better than just returning false :)
p values are a measure of the accuracy of the numbers. They are measuring how close the sample mean is to the population mean. In the case of the paper, the p values represent how close the sample mean of the head gaze, eye gaze, smile intensity and smile duration measurements are to the population means of the same values.
http://en.wikipedia.org/wiki/P-value