One is a file path, the other is a route. One represents a physical path on the file system, the other represents a logical path in the software.
So while you may find an avatar on your file system, e.g. data/avatars/l/38/38615.jpg
, you won't find a path such as threads/route-filter-does-not-work-for-data-avatars.170569
or threads/170569
on your file system.