That appears to be an hg error message.

The git version is:

    $ git push github master
    To git@gitproxy:rip747/    cfwheels.git
    ! [rejected] master -> master (non-fast forward)
    error: failed to push some refs to ‘git@gitproxy:rip747/cfwheels.git’

That makes no mention of -f (or any git commands at all).