Fantasy creatures aren't mythical, they just discovered space travel first and emigrated.
So when man finally set off to pursue strange new worlds, he was going where gnome-man had gone before.
The half-life "Little Rocket Man" achievement is just a tip-of-the-[pointy]-hat to this great truth.
"Fun conspiracy theory #6,000,050"
[on rocket ship: "U.S.S. Pointy Hat"]