Powder..patch..ball FIRE!
It depends on the TEMPERATURE the unit was run at. The picture shows nothing more than water scale from heat, (lots of it). If they had used distilled water or even a commercial antifreeze as a transfer fluid the inside would probably be pristine.
The trouble with both of those options is tha you need a LOT of distilled water based on his tests, and if you are working on a test unit that will be opened and closed antifreeze is not fun or clean.
I would assume that the home units will have city or well water running through them. What are they going to look like after six months? And how do you know it's just water scale, and something else isn't involved? That's a lot of scale for a few hours operation.