The rust I had on my pool started out like this. I believe the water came from condensation between the liner and the wall. My liner had horizontal wrinkles in the wall from chronic low pH back when I was using 2 floaters packed full of trichlor to try and keep the chlorine up before I found TFP. My liner did not leak, but my rusted areas where always moist. From the photo the rust at the bottom looks like surface rust. There may be too much water pooling at the base of the pool when it rains. You'll need to check it next time it rains to see how long it takes to drain away from the base of the pool.
To make repairs you will need to drain at least half the water, below the rust spot on the middle of the wall. Hindsight being what it is and all, I would schedule a weekend with good weather and a few available friends to drain the pool completely, pull back the liner, sand off the rust inside and out, patch with sheet metal where needed, and hit the entire inside of the wall will rust inhibitor. Odds are the inside of the wall looks worse than the outside. If you registered the pool you may want to pursue a warranty claim and see if it is cost effective for you.
I've attached a photo of my former pool to show what the wall looked like where the rust started, and how the inside of the wall looked after the pool came down. You can see small "blisters" starting to form on the surface. They eventually turn into weeping rusted through spots if left untreated. Unfortunately I did not repair my rust problem and lost the pool.
There is a lot of condensation on the outside of the wall in this picture, but you can also see areas that look like a blister with a ring around them. That is how my rust spots looked at the beginning.
This is the largest area of rust I had. The rusted through portion where you can see liner poking out is about the size of a softball.
Outside section of wall with the torn edge where the rupture occurred.
Same section of wall flipped to show the inside. This is what was going on behind the liner on approximately 1/3 my pool wall.
It took about 5 years for my pool to get to point where it ruptured, so I don't think you need to drain and repair today, but pick a time where you can plan ahead, gather the help and materials you need and fix it right. Or look around and find someone to fix it if you don't want to do it yourself.
Here is some information on rust repair:
https://www.inyopools.com/Blog/advanced-wall-repair-on-an-above-ground-pool/