Why did John McCain use Walter Reed as a backdrop?

The "green screen" background that was shown on television was funny enough for its own reasons (if you are a Colbert fan you understand).

But... here is the full background that was shown behind his Maverickness...



It turns out that this is a picture of Walter Reed Middle School in North Hollywood.

Oh... that makes a lot of sense (I guess).

((and I thought it was just another one of his houses)).