That particular kayak is 35" wide which is almost the widest kayak made and the hull design is more of a pontoon shape so it is very stable and a raised seat of a few inches won't make it overly tippy.
It's true that the lower you sit at water level or just below is the most stable.
The wider kayaks get away with the raised seats because of the width, but they give up speed.
The narrower kayaks from 28" to say 30" aren't good candidates for raised seats, but they are better in the speed and glide department.
With kayaks everything has a trade off, and that is why you will hear that there is no such thing as the perfect kayak that can do everything well.
Stability, speed, manuverablility weight are hard to put into one package, but you can come close. It's just a matter of matching the kayak to the type of fishing and waters you will be fishing.

Glad to hear you didn't have the back pain with your new setup.

Forgive me asking this, since I'm a kayak neophyte.

But, doesn't putting a raised seat like that raise your center of gravity enormously?

Still, looks like a cool solution to avoiding a wet butt.

I had an Ocean Kayak Caper a few years back and I placed a rubber seat cushion on the seat to help with butt pain, and it made my kayak tippy just those 3" higher. I got used to it and developed some confidence, but I knew that I was pushing my luck as far as making it easier for me to turtle.
I'm pretty active when I'm fishing and I move around a lot, and even setting a hook got a few times got interesting and I almost went over.
I see guys out on the lake, and most aren't sitting way up there in those high seats. If you do, you had better know how to self rescue in deep water!