The problem is that "what sounds better" isn't the same question as "which one is uncompressed". The original CD version might have some high frequency stuff t

The problem is that "what sounds better" isn't the same question as "which one is uncompressed". The original CD version might have some high frequency stuff that's just on the edge of perception that you don't really know is there, but you can just sense a bit of discomfort when listening to it. After going through the MP3 process and that high frequency is removed because it contributes the least in reconstructing that signal, the resultant decompressed signal might sound "better" even though it's not the original, because you get a high quality reproduction but the thing that led to a slight discomfort when listening has now gone. In this case, the sound engineer got them all right because he could tell the difference and knew what it was supposed to sound like. The rest of the people maybe could tell the difference or maybe couldn't (which was the claimed result of the test), but in fact, even if they could tell the difference, they had no idea which one was the uncompressed one and voted on which they thought sounded best. As another comment has noted, it'd be a much better test if there was a "they sound the same" option as well as asking which one sounds best.