The reason the oil life dropped is because you must have went into regen right when you left the dealership.
The reason it drops so fast is due to fuel dilution. Fuel gets into your oil, and the computer accounts for this by taking % off your oil life. IMO when you're stock with an LMM you should have a mileage that you want to change it out normally at, and do it either when the DIC says, or when your mileage hits, whichever comes first. The computer takes into account fuel dilution which you picking an interval does not. I don't know about these other guys, but I don't want an extra half gallon of diesel fuel in with my oil
search around, there's threads about guys pulling out close to an extra gallon of oil than what they put in. Thats the kind of "unspoken" crappy thing about the DPF and regen. Since I'm DPF free, I just go by the DIC, and change it when it gets down below 30% which was still like 7000 miles on my last change. Plenty for me, and I don't even run synthetic.