I think there are 10 possible explanations here
An unknown and hitherto unexamined species of animal, closely related to man.
Some sort of supernatural being, perceived by only a few people.
A known animal, such as a bear, that has been misidentified.
A large primate that has escaped from a zoo.
A man in a gorilla suit perpetrating a hoax.
An extraterrestrial species that occasionally visits earth.
A mass media induced hallucination.
A drug induced hallucination (what are these guys doing in an airport anyway?!?)
A product of a mentally unstable mind.
Some other type of unexplainable event.