That would work IF the shape were a smooth oblate spheroid (plus craters, of course). It isn't.

A more complex development of the story would work if the moon spun-down while the liquid core was still present (at least a small one, or a mushy zone). As the moon spun-down and the surface shape CHANGED, the maximum change of curvature would be at the equator and the planet's crust would tend to fracture on an equatorial circumference. (With the crack working up from the base of the crust, and liquid being squeezed up into the crack as it grew.

THEN the mushy core stuff could ooze out of the crack, forming the equatorial ridge, like a continuous string of a volcano - on Earth, we call these "Fissure eruptions" where a dyke of molten Magma reaches the earth's surface and fountains and oozes out along a linear fissure. Kilauea volcano frequently exhibits fissure eruptions, but one stretching right round a moon's equator would be a hell of a sight. (But it would be a water eruption, not magma - but as with Enceladus, there would be geysers!)