It was once widely believed that Wayward Cave's small colony of Gible was descended from a small group who accidentally tunneled through the center of the Earth. Needless to say, this is a legend; the earth's core is molten and Wayward Cave is located in Sinnoh, which is a floating Torterra island not connected to the Earth's crust. But Gible do have a penchant for turning up in the strangest of places, and rarely by design; indeed, the first Gible probably arrived in that cave by accident.
Gible, like their evolved forms, have thrusters on the sides of their head which act essentially as jetpacks, although they are easily mistaken for ears. But while Gabite and Garchomp use their thrusters to boost their speed while running and aid them while hunting prey (or today, in pokemon battles) Gible burrow into the ground like Sandile and hope unsuspecting pokemon will walk into their jaws. The reason their thrusters develop so early is not to hunt, but to escape larger predators by rocketing through the ground or the air. But unlike their evolutions, Gible's round body and light weight are easily hurled high into the air, and these pokemon have little control over where they land.
Getting lost is rarely fatal for Gible, for these pokemon are remarkably adaptable. Even if they land in water, they are buoyant enough to float and water pokemon float by their mouths nearly as frequently as terrestrial pokemon do. Their only nemesis is the cold, and many have frozen from straying too far from the tropics, but if they can find a warm current or a heated cave this can be overcome. What needs explanation is not the Gible colony in Sinnoh, but why there are not more Gible colonies in other warm and distant lands..