Just because somebody denies the truth does not make it not true. The US military denied the existence of, and obfuscated the development of the Stealth fighter F117. This aircraft:
They stopped denying it's existence in 1988. I joined the USMC in March of 1980, and upon returning from my AFUN training at NAS Memphis in October 1980, I personally watched an entire squadron of them performing in a secret air show (along with 3 battalions of Marine avionics specialists) at Twentynine Palms MCB. Having said that, people
cannot for one minute assume that representatives of the government (including artists contracted to decorate government buildings, or contractors hired to maintain or develop secret systems) are telling you everything they know. Doing so could get one the death penalty as a traitor. The trial and sentence can be carried out in secret and nobody would ever know the truth.
So...the mural means something. It is at this particular airport which is significant.