One can also use genuine Windows 7/8 product key to activate Windows 10. In fact, even today, PC users with genuine copies of Windows 7/8/8.1 are allowed to upgrade to Windows 10 for free although Microsoft has officially stopped the free upgrade program about a year ago.
Most of the home users have upgraded to Windows 10 using the free Windows 7/8/8.1 upgrade offer that Microsoft had started along with the release of Windows 10.
