First of all, what is a "bird hip" vs a "lizard hip"? It's a reference to whether the pubis bone points forward (as in lizard hips) or backwards (as in bird hips). Think of this as a general description of shape, like "square" vs "triangle"

Ancestrally, dinosaurs had lizard-like hips.

Early on dinosaurs split into two groups, "Bird hipped dinosaurs" and "lizard hipped dinosaurs". The "bird hipped dinosaurs" had birdlike hips, with the pubis pointing backwards. The "Lizard hipped dinosaurs" kept the original arrangement with the pubis bone pointing forward.

Later, a branch of the "lizard hipped dinosaurs" (the maniraptorians) independently transitioned from "lizard like hips" to "bird like hips". They were still in the "lizard hipped dinosaur" group because that is the ancestry they descended from. But they no longer had lizard like hips. One branch of this group went on to become birds.