Right....but your user shell has nothing to do with shellshock. Shellshock involves things like Apache invoking system calls that need a shell, and those system calls don't care what your user shell is. They care what /bin/sh and /bin/bash are (or wherever your system shells live, it's /bin for OSX).

This guide is claiming that updating your login shell to bash via Homebrew will mitigate shellshock, which is flat-out wrong, and dangerous to boot.