Almost every modern reference to "Corporations are now people!" is a callback to Citizens United. If the commenter I replied to is not aware of and was not referring to that, I apologize. But... he probably was. A simple search for "corporation are people" or "corporate personhood" will bring up articles that immediately and extensively focus on Citizens United.
And/or to Mitt Romney saying "corporations are people, my friend" which happened around the same time and this was a big political topic. The idea of corporate personhood became popularized around this time.
