Well spotted, but that’s actually an easter egg, not stolen art work (as devs can’t actually steal from themselves). The game is being developed by Robit Studios and Chucklefish (Developers of Starbound). Expect to find more of such easter eggs throughout the game.

If you’re interested, more info about the games development can be found here: http://treasureadventureworld.com/press.html

I’m afraid it’s just you. Itch.io’s a very reliable site. Maybe Itch.io downloads are blocked in your country? Could also be a problem with a pop-up blocker in your browser. Try using another browser and see how it goes. :)