I can believe that, something is necessary to cause any "dampness" to move into the atmosphere before it can be removed. The dehumidifier provides a hundred or so Watts but in a big space...
I was basing my thoughts on typical open sheds and barns where I've never seen dew form and any wet has to be blown in.
Slightly related but as a part of a project to check woodchip supplies I've had a kg of woodchip fuel, oven dried, sitting in this room. It's gone to 10% mc wwb in a week.
AJH