Even if this is a false reporting of storage, I wouldn't expect it to hold much anyways. 4GB is next to nothing nowadays. Most of that is likely going to be taken up by the OS, and the rest could be filled by just a few apps.
It is odd to see storage 100% full like that. My guess is it may be cached files taking up most of that space. Those can generally be cleared without worry, but it'll fill up again. Text messages can also do this over time if you don't delete them.