I too have walked into the room and saw a baby run across the room. Most likely got up through an empty feeder, or possibly a pan that was not fully pushed in all the way. Granted, it wasn't weeks old--maybe a day or two at most.
I also had a kit in a run who I didn't see for several days. Turns out there was a small section towards the back where the wall c-clips onto the run that a c-clip came loose, over the time the chins biting at it was able to pull a flap down. I never noticed it while cleaning cages... but it was just large enough for a baby to jump back and forth between cages. It took me a while to find her--most likely because she was constantly back and forth between the two cages at any given time and one female has not bred in 3 years--so I am not expecting anything from her.
It happens...rare but it does happen. I've heard of it happening several times to other breeders, and ranchers. Chins are escape artists, some more then others...
Could the OP be lying? Sure- perhaps she bred two of her chins and this is an excuse to post the cute babies and not get bashed. Or, perhaps a female was pregnant and littered without her knowing, and she didn't find the kit because she was not expecting to see a baby. Heck if its true and her boyfriend has been letting them out for the past several weeks on their own...there is the perfect chance for baby to get out. Considering they were let out in the evenings, and put away in the early morning---he had plenty of time to nurse from mom.