I wonder how it detected it though? The TV doesn't transmit anything, and surely if you're watching a dvd you're tv would still be receiving some signal? They might know you had the CRT on, but how detailed I wonder was the military tech?
They emitted cathodes which you could use to re-contruct the image. Or figure out what channel someone is watching.
But most devices do leak signals unintentionaly which can be tapped in to, sometimes even down the mains supply. It's all part of Tempest: https://en.wikipedia.org/wiki/Tempest_(codename)