The original artist had licensed it freely, both 2600 and the Trunk author had used that freely licensed work.
The argument they originally used seemed to be that the original work isn't actually worthy of copyright protection because it's just ink splotches.
> But it gets even better. You see, not only are they trying to get us to pay them for using a few ink splotches, but as it turns out, the ink splotches don't belong to them in the first place! Our cover artist happened to keep meticulous records (probably not something they anticipated) and traced the source of the ink splotches to a Finnish artist at this page. [3]
And as you can see below, the Loadus image (which is at least five years old) is a background to both our Spring 2012 cover and "Harry Potter in a Vest" or whatever Trunk Archive is calling their image (which also may not even be theirs).
No, they actually link to the original work, which if you follow, it's licence is pretty clear. Not reading the article the first time is fine (and common), but repeatedly insisting that people who have are in the wrong is kind of inexcusable.
Though, their tone elsewhere does indicate that they would have happily copied it, so you are partially right.