Definition of ROM (Read Only Memory) is that you can't change it. If maps and "other user data" are store in ROM, it can't be change; therefore worthless for any future uses.
Definition of RAM (Random Access Memory) can be taken as caching memory, normal memory and sometimes storage memory like SD related. Since 256 MB is way to much for caching (it will be expensive) it could be normal memory or storage memory. But giving the fact that ROM is already used for storing maps, there is no reason why this would be storage memory. So normal memory for program execution is correct.