Looks authentic. You can usually tell by the pebble leather quality. I have about 9-10 Alexander Wang bags - funny enough some come with the "made in china" tag and others don't. Other details to look for are in the zipper and logo. The "feet" are also similar to the Rockie I bought last year - though they vary from the First Edition Diego I have. Overall - everything in the ebay listing seems to add up.
Just in case you can ask the seller where and when they bought their bag. Hope this helps and good luck!