If the rest of the vehicle is not oxidized it is likely something else. Most of the time the rocker panels on daily driven vehicles will have a combination of road rash, rock chips, road film, dirt embedded paint, along with embedded road tar and brake dust.
The best way to see what you are working with is to thoroughly clean the area and decontaminate the paint. Something like CarPro TRIX followed by claybar decon would be a great start. Once you get down to clean, bare paint you will be able to assess what level of compounding or polishing needs to be done to restore the paint to it's former glory.
