There's another comment that has a pretty good theory -- the form the tool uses probably has a field that asks you to fill in who requested the file(s) be removed.
(The dropbox guy already has said he used an internal tool developed to remove files, without realizing that it would send this DMCA notice notice.)
(The dropbox guy already has said he used an internal tool developed to remove files, without realizing that it would send this DMCA notice notice.)