Find uses access(2) to implement -readable. Unfortunately that doesn't actually translate into a guarantee that the file can really be read by the find process (or the user running it) among other reasons because NFS clients have no way (in NFS <= 3 at least) to apply the same set of access control checks that the server does. Root squashing, for example.
So while, yes, a clearer description would be helpful, it's not quite as simple as "by whom". As always, a specific suggestion for a change in the form of a patch is very welcome.
