Bicycle detail

parked my bike at work by my entrance door, and when I came back for it, my bike was gone (had a rack and basket on the back with my helmet, a patch kit, and a ski mask in it) and my lock was left where the bike was parked. I'm not sure what happened, I am pretty confident I locked the frame to the bike parking stall appropriately but perhaps not through my wheel, I usually feel like my bikes pretty safe bc it's next to the front door of my office (there's 3 other racks between mine and the neighboring street), so I don't worry too much usually about how much I jumble my numbers, so they may have been able to get it loose or something? not sure. it was a chain lock with a 6 number combo lock. I reported to campus PD immediately.