How are Bigfoot and the Loch Ness Monster different from alien abduction stories and Elvis sightings? They’re similar in nature, but there’s just enough likelihood and potentially credible evidence for Bigfoot and Nessie to take them to a different level, one where reasonable people might believe that they’re imaginary, but can’t completely dismiss the possibility that they aren’t.
Mokele-mbembe may be on a third level, one where it’s not only possible but even somewhat likely that it exists.
It’s stuff like this that keeps people like me fascinated by science. Just when we think that we as a race know pretty much everything, something comes along to rock our worldview and show us just how wrong we are.