It's killcam lag as far as I can tell. Killcams seem to be generated locally, while deaths are worked out host-side.
As a result, you were likely killed just as you entered the bulding, but in the time it took for the information to reach you, you had carried on inside. Upon dying, the killcam uses data on your end (the incorrect data) to represent visually what it thinks happened. It takes the means of death (correct) from the host, but the your latest x,y,z information (incorrect) from the victim.
Killcams are not recordings, but rebult representations that should be taken with a grain of salt. On the killer's end, you'll have died a good half second before you did on your end. I've hit people with poles before who carried on walking for a good 2 seconds before they dropped due to lag. I imagine the killcams were pretty freaky in those situations.