Well, my first thought was this is Disney's excuse to include a non-canon creature in a land based on Cameron's world and let Cameron approve it.
Disney thought it was a cool effect. Cameron probably agreed. And they worked out an excuse to include it. Just like their excuse to have breathable air. These are just backward explanations for what and how we're experiencing fun stuff.
That all said. A plaque would be nice. There's plenty of chalkboards, signs, and diagrams explaining conservation efforts, species, and animal facts in all the Animal Kingdom animal exhibits, so not sure why this one should be any different.