They weren't too friendly with each other and in flashpoint paradox their war had destroyed half the world(I know that the conditions were different in it but bear with me). This would make complete sense because batman could be explaining Diana that their war could end the world, and how does he know that you ask? Because he's BATMAN! So the destruction we see could be the evidence of the war! And also, Diana was carrying shield and sword along with her regular lasso and eternal beauty(it's actually eternal), which we have only seen when she's fighting with her fellow amazons! Think about it and tell me what your thoughts.