Based on the question provided, I can't really tell what the stated goal is, but what it sounds like to me is a form of pre-exhaustion training.
Pre-exhaustion training is basically doing an isolation movement of some kind to weaken (pre-exhaust) a targeted set of muscle groups before moving on to a compound muscle group, or in this case a static movement used to pre-exhaust before moving to the dynamic movement. The end result is the secondary movement itself is more difficult, and in some cases, weaker muscle groups will be more utilized because the dominating muscle group is now too weak to compensate. In theory, this will maximize muscle recruitment while simultaneously making the exercise safer because you'd be using less weight and/or less reps.
It is a common technique used in advanced lifters to make a compound movements more effective with less weight. It's also used to weaken dominant muscle groups so the targeted muscle groups can be better used. For example, I've been training in powerlifting for many years, so my traps have a tendency to take over when doing something like dumbell lateral raises. I want to do lateral raises to target my shoulders, so I can do really high-volume shrugs to "pre-exhaust" my traps so I'm forced to use my shoulders during the lateral raises.
In this specific case, in mixing wall-sits with squat jumps, it could be the coach that wrote the program is wanting you to pre-exhaust your legs and glutes with the wall-sits. Then it would require more muscle recruitment to get the same kind of force during the squat jumps.
Or (s)he simply wanted to add more volume to the set so you only have to do half the amount of squat jumps.