Part of it is that he's comparing his work-from-home AC expenses to his work-from-office gas expenses. He's not factoring in the
company's office AC bill, because he doesn't pay it.
Also note that, at least in my case, I've got a cubicle farm at work. I can't just up the temperature for my 64 sqft cube; I have to up it for an entire quadrant of the floor.