Tilt the pelvis, keep the upper body organized
Imagine your pelvis as a bowl: As you tilt it forward, the front edge lowers slightly while the back edge rises. This makes your butt look slightly lifted. As you bring it back, the bowl returns to its starting position. For this first exercise, the movement ends there, without tilting further back. Here, tilting forward means changing the angle of your pelvis, not pushing your entire hips forward.
Your pelvis and lower back do not move completely independently of each other. So a small change in the curve of your lower back is not automatically wrong. The problem comes when you imitate the movement by pushing your chest up, flaring your ribs forward and drawing your head back to create a bigger effect. Then it is hard to tell what your pelvis is actually doing. Keep your neck long and your abs active enough that you can continue breathing calmly.
The visible pop comes from a short, clearly defined movement impulse. Knee-driven shakes are a different task; the basics of different twerk movements can help you understand the difference. It makes sense that even a small isolation can be tiring, given the difference between coordination and physical exertion when dancing: Bigger movements are not automatically better exercises.

