Downloaded WOTLK File Cannot be opened - HELP

I have downloaded the Wotlk file given on this website with Bittorrent on my Macbook air. The file looks good and complete to me, but I just can't open it. It'll always say ' The program World... cannot be opened'. I figured that it might be due to my macbook, maybe it is too weak or the file is damaged.. I don't know. I am not that much of a computer freak so I'd really appreciate if anyone could help me out here. I do have installed the Mac version though.

1,4 GHz Intel Core i5
8 GB 1600 MHz DDR3
Macintosh HD
Intel HD Graphics 5000 1536 MB

Thank you in advance!

Did you make sure to download a MacOS copy of your WOTLK?
A Windows/PC copy will not work on a Macbook without Bootcamp.

Yes of course I did.