The holes in acoustic string instruments are not there to "allow sound to escape". Sound radiates in all directions from the surface of the instrument, although the frequency balance may change from point to point. Consider drums, for example. A drum may be completely sealed, yet still work and still make sound.
The purpose of soundholes is tuning the resonant frequency of the acoustic chamber. Google Helmholtz resonators for the theory and math if you like. The area and depth of the port alters the resonant frequency, which is largely a function of volume.
Acoustic guitars usually have large, circular holes. When recording acoustic guitars, you should never point the microphone at the soundhole! You'll get a dull, woofy, severely unbalanced sound. There are many mic techniques to deal with the frequency issues, but the most common is a microphone along the neck, aimed backward at the neck/body joint. That wouldn't work if the sound just escaped from the soundhole, as the article implies.