
Orca pods (alongside most other cetaitions) have complex social hierarchy and language structures. Calfs are given names and raised to maturity with only the males being kicked out.
Different pods have different accents and the further two pods are away from each other, the less they can understand each other! Their language is so complex they've essentially developed multiple mutually unintelligible languages!
ML's mother would have definitely given him a specialized click that would be his name. Unless he was orphned so young he never learned it. But that doesn't seem to be the case given how he speaks of the ocean.
Sejin was being WAY too generous but that shows character imo. Even though Ido hurt him so deeply, he won't force him through pain, because he doesn't have the heart to be so cruel.