At that time there were no resin wall pools on the market so stating a pool was resin or hybrid automatically meant top rails & uprights & a coated steel or aluminum wall.Full resin in this case meant no steel plates or bottom rails either.
I am surprised though that there were no mentions of the wall material or touting of its special coatings & such as most do.
The matrix is a good pool with a good reputation but any steel walled pool is susceptible to rust when moisture is involved.
The only resin walled pool available that I’m aware of is the Aurora & it just came out in the last year or so.
I wouldn’t be surprised if multiple other manufacturers come out with resin walled models in the near future since I believe the Aurora has been selling like hot cakes.
It looks like there have been several leaks over time in your pool that have allowed rust to take over. Even if you have a resin walled pool unchecked/ un repaired leaks can undermine the pool’s structural foundation & lead to collapse.
Let us know how the warranty claim goes.