Why is it saying install size only 7MB, takes a few minutes to install, says complete but no change?

The installer downloads after a few hours, installer .dmg size is 6.2GB, .pkg is 6.21GB

After launching the El Capitan InstallMacOSX.pkg, it tells me it will run a check to see if it will work on my computer, I continue to next step and it says space required is 7MB location on Macintosh HD.

I dont get why this is, I say continue so it does it's thing installing something for a few minutes and says completed, then to exit.

After exit, nothing, restart does nothing, nothing changes... Am I supposed burn the DMG file to external DVD or make a bootable USB because the instruction on this page say only to download and run it... Not a very effective installer...

I own a mid-2009 13" macbook pro running Yosemite