There are different populations of orcas that behave very differently. Some orca cultures hunt mammals, some are strictly fish specialists. Dolphins don't have anything to fear from the salmon-eaters, and dolphins are easily smart enough to understand which sort of orca they're dealing with.

It's true; orcas are the largest species of dolphin.

Indeed, orcas are a very large dolphin species. Some orca populations behave differently than the orcas in the article -- they hunt mammals like sea lions, seals, and smaller dolphins. Dolphins are well advised to stay away from the orca groups that eat mammals.