WoW Insider was alerted to the presence of this installer on battle.net. It's apparently there for every account, even starter editions with no World of Warcraft license. Its presence should not, therefore, be taken as any indication of alpha invitations being sent out or access granted.
Nonetheless, the installer is downloadable, and runs, as can be seen below. It appears to be a 24.48GB download, so the CASC file system's smaller size will likely not be seen at the install stage.
This definitely is not a mis-labelled PTR, either, as it doesn't replace them on the game list in the launcher, and launching it from the desktop app gets you to a set of servers
that just don't seem to work, so it looks like access is not set up just yet. Closing that window will put you back to the Warlords of Draenor
alpha-style Dark Portal login screen. There is not access to the game at this point.
[Thanks for the tip, @Spazzo!]