I doubt they used any foam on the backsides of that material.
I've seen 1/4" then they run the skiver over the material and it will remove the foam in their seam allowance.

do you think they attached the scrimm foam on the seat foam?

What I typically do, which is tedious and time consuming is after pieces are sewn together I go back and cut the foam away from the seam allowance. That makes it so French Seam is seen through only one side of foam allowing seam to lay flatter. I also stick with the same thickness of scrim back foam on both sides of seam if I were to French seam

I recently did these did 1/2 scrimm foam at tops and 1/4 sides and cut off the foam from the seam allowence but I still fill they are bulky.

I find 1/2 scrim foam to be too thick to be using with a French seam. It leaves it looking puffy in my opinion. I usually use 1/4 or 3/8 scrim foam.