The Sea Demon Clan is called a civilization not only because this species possesses intelligence, but also because they've developed a cultural and ethical system through historical accumulation.
It's precisely due to this characteristic of being a "civilization" that allows civilizations to communicate and understand each other, avoiding friction and conflict.
Of course, the premise is that there is no conflict of interest between the two civilizations.
Humans and the Sea Demon Clan belong to different worlds, and there's no irreconcilable conflict of interest between them.
Therefore, in terms of survival space, humans and the Sea Demon Clan will not form a hostile relationship.
As long as it's not a hostile relationship, communication is possible.
Moreover, with the appearance of Liu Haiyang and the other five, helping the Sea Demon Clan kill the mad sea beasts, they have gained some recognition from the Sea Demons.
This is a good start.