Better get a reply in just to make sure then

Came here looking for factorio. Great game and possibly the most stable piece of software I've come across

Is it though?

Theft in Scots Law is defined as the wrongful appropriation of the property of another, with the intention of permanently depriving the other person of his or her possession.

source

Pretty sure that you do have to intend to permanently deprive for it to be theft. What you're describing is copyright infringement. Whether that's morally right is a different question but it's not stealing.