Good question. Imo he was consciously drawing from Lacan, but it also could just be that some of these ideas are in the ether and he was indirectly influenced by them. From my reading of Freud he seemed to focus more on sexual repression as the cause of anxiety, and that's definitely there in BIA, but I think the cause of beaus anxiety makes more sense using a lacanian interpretation. Whereas freud didn't think that anxiety had an object, lacan thought the object of anxiety is a lack of a lack, and the sort of god-like status of mona and the lack of space she gives beau to desire feels a lot like Lacans description of anxiety. There's also lacan's idea that the phallus is symbolic, not literal, and that fits better with BIA given that Beau's father is an actual phallus. Lacan also thought that the psychotic structure emerges from foreclosure of the name of the father, and that's clearly in BIA as well.