It's a True Story!

Imagine, if you will, a dark morning. Tongo (the dog) is running around the house looking for an open door and a fresh face to lick. Mom is downstairs, getting the downstairs presentable for whomever decides to wake up next. The sun has barely risen.
Dad wakes up to Tongo's jingling dog tags, and decides it's time to get up. He stumbles around in the dark, looking for his clothes. Tongo is sitting on the bed, doing anything but minding her own business.
Mom opens the bedroom door to see my dad standing in his underwear, stumbling into a pair of pants; Tongo sitting on the bed; the lights are out.
Dad glances to the door and sees mom standing there and quickly explains, "I thought you were asleep. . .I didn't want to turn on the light. . .I thought the dog was off her leash."
My mom just stands there, on the verge of laughing, and my dad adds very defensively, "It's a true story!"

What we're wondering, now, as we laugh at this is: What does he think the fake story was?