Shouldn't git-ls-files --others use $GIT_DIR?

If I do

GIT_DIR=$HOME/projects/<project>/.git git ls-files --others

from, e.g., $HOME, I get a list of all the files in $HOME and its
subdirectories that aren't in said git repository.  Shouldn't --others
use $GIT_DIR, instead of ".", or am I missing something here?