This may prove useful in in the event you absolutely must open a bottle of wine but have no corkscrew.
Technically a shoe and a wall. My French is pretty much limited* to Je ne parle pas Français (and croissant, so I would never say Je ne parle pas croissant) so I assume the narrator is telling you that pressure is force/area, and so any force you exert on the liquid at the base by whacking the bottom of the bottle will result in a much larger force being transmitted to the cork owing to the reduction in area.
What he is probably not telling you is that this is a poor technique for ketchup, and not because French cuisine and ketchup are incompatible or that it won’t work on screw tops (both true) but that ketchup is a non-Newtonian fluid, and when the ketchup clogs the neck of the bottle it prevents air from entering, which is necessary to let the ketchup flow. Don’t invert and bang on the bottom (this holds true for more than ketchup, but I digress). Hold it with the open end down at 45º and tap the neck to induce the shear-thinning.
(*My limited vocabulary also allows me to get the following joke: Why do French omelettes have only one egg? Because in France one egg is un oeuf.)