All of the previous comments are spot on, the appraiser bases his/her numbers on recent similar units in the building.
That said, a) you have the right to contest it, request a copy, and, b) it is very possible the appraiser doesn't know what he/she is doing. Finally, truth be told that building has suffered quite a few short sales and/or foreclosures and many of the units are outdated.
When I checked for "overall sales" in that building in the past 6 months the "median" came in at $116k and the average at $135k! Based on this I would say you got a good appraisal.