I believe the whole situation is this.

The flood happened reducing the ondo's entire territory to an incredibly small space compared to what it was.

The flood was caused by finless ones.

We and Bismarck put an air bubble where they hunt and breed.

We never interact with the Beashos in the msq prior to this.

It could be interred that they only knew finless ones caused the air bubble which reduced their food supply and made birthing much much harder.

So they have just cause to want vengeance against finless ones just it should be more directed at us but they may not know that.

The queen was going to use the eggs to make an army for war against innocent people.

Norv is a sahagin that went against his people's desire and raised his eggs to be more welcoming to other races.

While it is not stated I suspect there would be some Beashos that might've gone against what the queen had planned and could've raised some to be better, but there is no hope now since all gone and most likely make themcall hostile now.