Falsely claimed successful install of El Capitan

I have Mountain Lion 8.5.

From article HT206886, I downloaded the file InstallMacOSX.dmg from where is said: use this link: "Download OS X El Capitan."

I extracted and ran InstallMacOSX.pkg.

After following the directions, it said "successful."

Unfortunately, nothing changed; I was still on Mountain Lion 8.5.

The log contained the message: "installed is not entitled for system.install.apple-software."

What is wrong?