I’m missing how this is groundbreaking or even a “conversation”. They played audio recordings of other whales to the whale and it replied the way whales reply to one another. The scientists didn’t know what they were saying, other than since the target whale appeared to stick around it probably wasn’t completely gibberish.
Whether this is groundbreaking or not depends on what the whale thought of it. If it got the notion that humans are now actually trying to talk to it in its language, I'd call that a win.
To me, it seems like precisely this part got lost in translation