A day after the promotion had begun, a forum member posted an e-mail they received from GOG's support staff, which explained that the free games were obtainable "due to a small glitch on our end." While the email explained GOG would remove games the erroneously-free games from a customer's shelf if they so desired, it also stressed that "it's totally cool with [GOG]" if a user would prefer to keep them. Class acts then, all the way around.
If you're interested in actually purchasing games from the sale, the Linux Launch promotion will last until 12 a.m. EST Tuesday. Don't Starve, Kentucky Route Zero and Sir, You Are Being Hunted are among the sale's offerings.