Per Rob, the maintenance guy at Missoula International Airport, the sink in the men's restroom on the upper level originally had a mirror. The problem for some travelers was that from outside the restroom people could see men using the restroom through the reflection in the mirror. So, maintenance installed a privacy partition on both sides of the mirror to ensure no passersby would be corrupted or tempted by glances or glares into the chamber. (I guess, in Missoula it drew a crowd.) The mirror has temporarily been removed by maintenance for unspecified reasons. The privacy partitions remain because the mirror may eventually be replaced/reinstalled and because the adjacent mirror may also present a partial view.
So, was it an eye-full of burly manhood or a some teenage wanker that drove some poor prudes to complain? One can only imagine.