To elaborate on the Virdis Leo, which is the alchemy thing, real quick, it is a lion that is typically green (hence the Virdis part). However, once it eats the sun, its body is purified (hence the white coloration), and it glows gold.
As for the Great Moon Hoax, back in 1835, a fake news story was published under the name Sir John Herschel (he was a respected astronomer at the time). However, Herschel did not write the story, it was just written using his name to give the entirely fictitious claim credibility.
The story told of how "Herschel" used a very advanced telescope to survey the surface of the Moon, we he found life. There were goats, bison, beavers without tails that walked on two legs, and the coup de gras,
bat people. Keep in mind that this was published in an actual newspaper (funnily enough, the paper was named "The Sun").
Here's a depiction of one of these bat people. Notice any similarities to Lunaala (sans the beard and such)?
https://upload.wikimedia.org/wikipe...eat-moon-hoax-new-inhabitants-of-the-moon.png
This inspiration would make sense, as both Solgaleo and Lunaala would have taken inspiration from claims derived from debunked psuedo-science.