System restore doesn't equal reset.. now it makes sense.
You don't need to buy win 10 again, when you upgraded first time you got a digital entitlement to always install win 10 on PC again
Download the
Windows 10 media creation tool and use it to make a win 10 installer on USB. You can use it to upgrade current PC or since you just did a reset, you might be better fresh installing it and then next time you factory reset, it won't go back to win 8 again.
If you want to fresh install, you would need to wipe drive. if you had any other partitions on drive that had data on them, i would copy it off first
Guide to clean install:
http://www.tenforums.com/tutorials/1950-windows-10-clean-install.html
When you reach screen asking for licence, click "I don't have a key" and PC should auto activate once win 10 installed.