It’s yet another way Snyder has shown support for those who would like to see what his original vision of Justice League would have looked like, as the final product both critically and commercially underperformed.
(Does that make Warner Bros or people who deny that the Snyder Cut exists the devil in this scenario?)
It’s not hard to put two and two together here, with the Holy Grail serving as a metaphor for the Snyder Cut and for fans to keep up their efforts to get it released.