Without intent, it isn't theft. Feel free to cite California law, but in Texas:
The fact is that he has software that doesn't belong to him, can't explain how it got there, and that's illegal.
You must have missed this part of the article:
We pass our old computers down. The guys in engineering need a new PC, so they get one and we pass theirs on to somebody doing clerical work. Well, if you don't wipe the hard drive on that PC, that's a violation. Even if they can tell a piece of software isn't being used, it's still a violation if it's on that hard drive.