Water Damage Source

In my wife's office, a single story wood frame on slab built around 1980, there appears to be water damage to the sheetrock about 8" up from the floor on a partition wall about 8" from where it intersects with the outside wall. At first glance I thought it could be roof leaks but there is no staining on the ceiling or water on the floor on either side of the partition wall. I looked outside and there's a PVC condensate drain at more or less floor level coming through the exterior wall. The drain is running inside the partition wall from an AHU to the outside. Is there anyway that could be the culprit? I really don't see how, just an odd coincidence, maybe.