perhaps its a proxy download? that is, it basically downloads a downloader. pretty common with larger games, as it tends to use less data. Nutaku uses them exclusively. then the game itself installs over the downloader.
that said, i'd recommend trying the download over data/wifi (whichever you havent yet, if either). push comes to shove, i had to download the APK to my computer, then move it over to my phone. (side note, i tried it to help you. my phone doesn't have the guts to actually run it, but it did install for me, that way).