I think they might be confused because Pirating a game or playing a pirated game IS ILLEGAL- people don't normally play pirated games on a public platform for this reason.
Not only that it's releasing a build not released to the public for free, when you have to pay to get access to it.
Sure it's advertising your game, but they still released a beta build not available to the general public to their followers without your PERMISSION. You could legit sue them for this, good intentions or not.
if this person is pirating games or just playing them, I certainly hope they don't think they can get away with doing the same with companies games that would LEGIT SUE them for it.