Why does new file created by touch have GID wheel?
/var/tmp
has the sticky bit set:
pse@Mithos:~$ ll -d /var/tmp
drwxrwxrwt 5 root wheel 170 Dec 24 16:17 /var/tmp/
so any files created in there inherit the group of the directory.
From man sticky
:
A directory whose `sticky bit' is set becomes an append-only directory, or, more accurately, a directory in which the deletion of files is restricted. A file in a sticky directory may only be removed or renamed by a user if the user has write permission for the directory and the user is the owner of the file, the owner of the directory, or the super-user. This feature is usefully applied to directories such as /tmp which must be publicly writable but should deny users the license to arbitrarily delete or rename each others' files.
Any user may create a sticky directory. See chmod(1) for details about modifying file modes.