Seen this pattern many times in workouts, and it indeed feels effective. I would like to read more about it but don't know what it's called and explosive isometrics seems to mean something else.
If you enjoy this programming concept, go for it. However, keep in mind that in the fitness world, the gurus are under constant pressure to produce new tricks. How about squat jumps with a kettlebell swing? How about a squat jump and then you grab on to a pull bar and do fifteen pull ups (which I saw recently)? How about a squat jump and in the air you throw a medicine ball to a friend who catches it and throws it back? How about a squat jump with a resistance band around your knees? Anyone can make this stuff up.
As far as scientific research, I can pretty much guarantee that no one has done research on this type of "explosive isometrics" (or whatever you call it). The reason I can say this is that it would take a year or two to produce a research paper on the topic, and by that time the fitness world will have moved on to something new. Researchers can't possibly keep up with the latest bells and whistles that the Youtube gurus come up with. My point is don't expect anyone to have solid information about this topic.
So, have fun with it. I predict you'll try it for a few weeks and then move on. Let us know how it goes!
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.
If it feels like it works it probably does.
Do it often and get the most out of it. A static demand leads to adaptations biased towards static strength, which should directly oppose explosive movement, thus your body develops more of the ability to overcome its own rigidity. Doing the opposite sequence should require the body to get control of the dynamic stuff going on in the body.
If it works it works. Give it a month and do it 6x a week ha. See how your performance improves right after and a week after this leg intensive training. Test before and after training it diligently with a few agility tests such as the 5 - 0 - 5, strength test for 1 rep max, and an endurance test for body weight ATG squat count within 10 minutes or something.