in the episode The Armageddon Factor, the guardian is initially dressed much like the heart of wal-mart, and in ep 6 he can change his form or shape at will, and appears as the president of gallifrey not to alarm the doctor. the doctor acknowledges the guardian isn't who he says he is and the guardian reveals his true form.
The way Mr. Garrison announces that the Walmart is opening saying "it's happening" is similar to when the mole announces Bambi's birth at the beginning.