I'd award them for coming up with a good plan.
As you say, if the Johnson only suspected what was on the disk and had no way of knowing what the contents actually were, I can't think of a reason why the Johnson wouldn't be happy when the team delivers what he asked for; a disk with Jet Black music on it. That being said, the Johnson might be suspicious if he knew some details about what was supposed to be on the disk (track names, lyrics, etc), but discover those things aren't there.
To my mind, this boils down to how much information Mr. Johnson was working off of, and that is entirely up to you. If you decide he only knew that there was a disk with music on it out there, I'd reward the players for being clever. If you decide Mr. Johnson actually knew what the contents were supposed to be, the sky is the limit for how offended the Johnson may or may not be.