file gets its results from
application/msword doc dot
mimetype gets it from ...
These variables can list base directories to search for data files.
The shared mime-info will be expected in the "mime" sub directory
of one of these directories. If these are not set, there will be
searched for the following directories:
See also the "XDG Base Directory Specification"
Worth noting is this part in the man page for mimetype:
For naming switches I followed the manpage of file(1) version 4.02 when possible. They seem to differ completely from the spec in the 'utilities' chapter of IEEE Std 1003.1-2001 (POSIX).
So you might call it a bug against file
vnd.ms-excel is more accurate.