There IS a simple answer. (I’m reading “the mystery deepens” on news articles about such events as seals & smaller whales protected by bigger ones)
Orcas are killers, they kill what they can. But they can also kill white sharks, giant squids, and they do it regularly. Isn’t it right that whales have an interest in protecting their kind (mammals) by “teaching” the killer mammal who naturally does not make differences to favor preys that are not mammals and that represent a threat to their own progeniture ?