Alternatively, could it be the user is referring to Android 11 SDK version 30? Or maybe they're thinking of a codename or build number. Sometimes software uses build numbers that might not align with the public version numbers. For example, Android N (7.0) had build numbers like NPJ48C. So maybe there's a build version 511? That's a stretch. Alternatively, maybe the user is referring to Chrome 85.0.4183.71 or similar but misremembering the number as 511.