Aquaman speaks to Diana:
Aquaman: I hate Atlanteans as much as you Amazons do.
What's the story behind Amazons hating Atlanteans?
In Zack Snyder's Justice League, Diana told Bruce that the Amazons went to war with the Atlanteans once.
DIANA: Atlanteans can be tricky. My people went to war with them once.
They didn't reveal any more about the specifics of that war, but it likely happened some time after they teamed up with the Olympian gods and humans against Darkseid's forces, and the statement you quoted from the same film obviously implies that there's still bad blood between the two races over the conflict.