So, how did kangaroos get to their "hop"?

...through walking. The sthenurines, the ancestor of the kangaroo, were bipedal walkers - similar to many dinosaurs.

Maybe. It's still controversial, but scientists are pretty sure that they didn't hop. Which makes sense. Hopping, after all, is a strange way of getting around, and isn't something that a quadruped would ever invent. A biped, however...