People being fooled by this isn't a surprise, the technique the producers use to film this documentary is designed intentionally to mimic that of a non-fiction documentary. Actors play out fictional characters who give first hand accounts, often emotively and passionately and others play scientists and officials who speak in past-tense rather than theorise. All this, of course, is supplemented with fake news broadcast footage and images of newspaper headlines.
There was a recent attempt with this style a few years back involving the discovery of a dragon frozen in a glacier. For people who tune in mid-way through, you could easily mistake the thing for a 'breakthrough discovery'.
As for this particular documentary, it provides a rational account as to how mermaids could exist and it was actually quite enjoyable. These stories and myths are so familiar to us, so well versed that part of us wants to believe them and if we were given a reason to do so in the form of scientific evidence, we'd readily accept it.
