Mod as in casemodding. I agree, it should have been clarified, but I don't think any of us lost seconds off our life when we mistakenly thought that the DS was able to play Super Famicom games and found out it was merely a (admittedly kickass) casemod. I mean, come on.
Well, "mod" is shortened for "modification", so it's fair to say that this is a mod. If you take a look at this and don't think that it's modified, that's your problem.
So...your mom changing the computer's wallpaper makes her a modder. An exciting time we live in, no?