[T.G]

Yes, based on your description, it does sound like they might be using tap water with a high mineral content in the humidification system. The cigars closer to the humidifier would tend to display heavier or more deposits. Also, it tends to settle on the upward / outward facing of the cigar, similar to how dust would settle in a room, and, if you were to dig down to a lower layer in a box, you shouldn't find much in the way of these deposits.

While not terminal, it's not ideal for the cigars and might affect flavor over a long period of time. Obviously, cello and sealed boxes will be less vulnerable.