Also, I doubt that illegal aliens are Nielsen households, so the actual viewership would have been a bit higher.
Finally, here on the East Coast, the game was on from 5 AM to 7 AM. Turning it on instead of watching the local news repeat the weather and traffic every ten minutes wasn't that difficult. I find soccer generally dull, but for one morning it was something more interesting to watch.
My guess is that the people in 997,995 of those households fell asleep in front of their TV watching Leno or Letterman and the TV was on when the soccer match started.