hey, isn't this what we call a win-win situation? 😉
You are right, but if you have a Bandcamp account, the download code gives you the advantages of a paid download: the album shows up in your collection and you can appear in the “supported by” section on the album page.
(I may be wrong, I don't have a Bandcamp account myself)
But the main reason for this contest is the hope that the message will become viral and that it will promote the album.