Game of Thrones has undoubtedly generated a lot of money for HBO; perhaps pouring some of that into the finale to preserve secrets is an investment Bloys would be willing to make.
That said, he hadn’t read the finale script at that point, so he may not have known the plans Bloys and Co. had in place.
Admittedly, Nikolaj Coster-Waldau, who plays Jaime Lannister, disputed that claim shortly after Casey Bloys teased the multiple endings, arguing that HBO was not going to waste a ton of money just to preserve a twist.