Basically, a fluid is matter which flows without resistance to external stress from shear forces. The difference between a liquid and gas is a gas has no surface tension. However, at the masses and velocities involved in orbital impacts, surface tension is trivial compared to the inertia of the atoms. The main difference between a meteor impacting gas or liquid is the greater inertia of the liquid, with the surface tension contributing comparatively trivial resistance. With the examples of slapping the water or doing a high dive or a HALO drop into water, the surface tension is more relevant, but still less than the inertia of the water molecules.
High-altitude low-opening parachutists are taught to drop their packs into the water after opening their chute, both to break the surface tension and get the water directly below them moving out of their way. Otherwise they can potentially break their legs or spine.
