I've got another less exciting reason how it ended up there... someone at Sony or one of their contractors found it on here: http://www.iconarchive.com/show/oxygen-icons-by-oxygen-icons... It says there "commercial usage allowed". They probably didn't even know it was from KDE.
What if I go to some site, that offers me movies for free and states "commercial usage allowed" ?
And in any case, Sony can use this artwork commercially. It's free software, for goodness sake. What they missed was the requirement for attribution. So they should provide that somewhere. End of story.
I don't understand this kind of logic. I mean, I can see the hypocrisy argument -- Sony is a Big Evil Corporation and constantly harping about IP rights, and here they got caught not-quite-following-the-letter-of-the-licesense.
But come on now: the KDE team drew and released those icons (and the rest of their software) with the clear intent that they would be useful to people in their own work. They even licensed it to allow that. This isn't a great crime, it's just a mistake.