It is liquid fueled. I believe it is powered by hydrogen peroxide spayed on a catalyst inside a combustion chamber on each wingtip. It's like having a bombardier beetle on each end.
PS sometimes had the vacuum cleaner hovercraft ads, but they were definitely a Boys' Life regular. Google Books finds the same ad with the same picture running from at least 1974-2007. The later ones have a URL but it's squatted now.
Boys' Life Dec 1974 page 81 has both the big hovercraft and the tabletop one, suitably filed under "gimmicks":