Frozen Coal - How is this possible?

I recently had 4-5 tons of coal frozen to the Right side of my dump trailer. It was preloaded @ 6pm was in the mid teens that night, and the attached pic was the result at 8am after some scraping from the tail end n side.
Before I quit my job, I thought I'd ask if this is possible without someone sticking a hose in the trailer and turning it on.
I had 3/4 of a gallon jug of calcium flakes on the floor, and used 2/3 of a gallon of antifreeze sprayed on both sides and the nose (28' trailer).
The orange line in the pic is how high the coal was frozen to the side. Not a nugget was stuck to the Left side.

am I paranoid or is someone trying to flip me?

 

Yeah older drivers are pissed off at me - i got a raise to 26% in 3 mo instead of 12... someone in the office must have told someone. i've been told by other drivers going down the road there are no bears n 2 mi later there's the DOT . Happened more than once too! I Never did like this local driving but its a good co. to work for

 

Yeah... I never hauled this kinda commodity in the winter. No wonder it pays better than scrap - its a real pain in these freezing temps. I was having a hard time wrapping my head around it freezing to one side of the trailer when both sides were treated exactly the same, but if the wind was hitting that side all night... I knew wind chill matters but wow.
Thanks for all the input guys - I sure appreciate it.
Its D&V Trucking Jokingypsy runningabout 40 dump trailers - all local