Moisture on vapor barrier

Hi, I recently found wet carpet in the corner of my daughter's second story bedroom. Both surfaces of that corner are exterior walls. Upon opening up the wall I discovered that only the warm side of the vapor barrier and the drywall were wet. The insulation and the studs are bone dry. Since there is no plumbing at this part of the house, this leads me to think this is a humidity problem. Am I correct? The humidistat for the adjacent bathroom reads 58. I also noticed that the vapor barrier was not secured with either acoustical sealant or tuck tape. Does that have a bearing on this? It could this be an attic issue?