The NFSv4 client is not dumb, as it implements delegations and can recall them from a client after they are granted.
Unlinking a file over NFS has also been implemented as renaming to a temporary file, so slight of hand intelligence was present in earlier versions.
Honestly, it would be pretty nice to have some sort of path locking and an ability to request delegation on NFS rather than have it be this automatic conflict-resolution style. But whatever, ultimately it works.