But the sonic bombs of death may well be real... real enough to cause a number of prominent mass strandings.
I'm still watching it on YouTube, but the point I take from it is that whatever these things are doing to whales and dolphins, a (Human-esqe) sentient species would be affected just as badly, if not worse. It tugs at the heartstrings of the viewers, maybe having them emphasize with the real cetacean victims... and the plot posits that the US Navy could panic into committing a cover up if it was discovered that these tests weren't just killing protected species... but they were also effectively massacring populations of the only other living branch of the Human family tree.
No way to buy off the survivors, no effective way to make reparations even if the tests were stopped, not even any clue that they were sentient in the first place (before the capture of a live specimen) and, perhaps pustulating away in the minds of the most cynical of the militarys top brass, no way in hell that they were going to admit it if there wasn't a chance that they could just pretend it didn't exist.