They will give anyone a free windows 10 license so that everyone can upgrade.
Idea behind that is so that they can get more people porting to W10 that way they are more likely to use the MS APP Market. From what I've read earlier, it doesn't matter if its pirated or not, the offer is to upgrade any windows < 10 for free and the offer is valid for 1 year. This does not mean you have to buy a license after 1 year.
http://venturebeat.com/2015/05/31/mi...ws-10-upgrade/