I'm going to throw an idea out here (and I've seen similar things happen with astrophotography)...
The moon was probably a fair bit brighter than the building.
If you got a little shake at some point during a long exposure, it could be sufficient to cause the brighter objects (i.e. moon) to blur, while the movement was too short to visible affect the lower lit objects.
I see similar things when doing astrophotography, where if I say bump the tripod during a long exposure, I get blurring of the brighter stars in the final image, while the weaker ones don't show any visible blurring.
e.g. if you have a 1/2 second exposure, and you for some reason got movement during 1/60 second, if the object is bright enough that 1/60 second will suffice for causing some smearing, while fainter objects won't record much light during that brief moment.
Hope that makes sense.