Solo tuning. He reads it in G, but his bass is tuned a step higher, so it gets transposed into A. Same with Edgar Meyer's recording.
Solo strings sound brighter, and project much better. Besides, he was probably set up this way in the rest of the recordings on that album, so it would be strange for him to change strings.
Well.....hmmm, now that I think of it, Joel tunes in fifths, right? I don't know much about fifth tuning methods, but I still think playing the piece in A makes more sense with a high A string than playing it in G.
If you're looking for the piano part in A minor (so you can play it in solo tuning), you can download it here for free.
http://doublebassblog.org/2006/08/ec...uble-bass.html