It might be the Julian date (I have no idea where the name comes from) which is just basically January 1st is 001, December 31st is 365, and the rest of the year is between. So this would be around December 15th.
We used it for food expirations on some things at the convenience store I used to work at.
I suspect they did it so people wouldn't be put off from buying something close to expiration.
In fairness to the people I worked for, they only put it on stuff with a short shelf life anyway, so it was all fairly close to expiring. Also, it was a convenience store. Most people ate it right away.