The size of the file is too large to be held within an integer value so the number is just wrapping around. (An 8 bit signed integer can only represent the values -2147483648 to 2147483647.) File sizes are getting so large so fast the coders of the server software haven't gotten to update the code yet.
The whole file is actually there... try downloading it with an ftp client and you will get it.
I don't recommend trying to download a large file like that with a web browser... they have the same integer value problem and in the end it will end up thinking you have a negative file size, so the final save will fail. Use an ftp program.