Sure, congrats for finding all those secrets! The other one is hard to obtain but if you boost yourself against the slanted download button from the right fast enough, you can go into the ceiling... If you need more tips, let me know!
Sorry if it's a bit underwhelming ^^ It was just supposed to be a little extra thing to do on the side for players who already played through the game.
Hu is the greeting people use on our discord server (it originated from someone mistyping "hi" and became a thing from there) Just a little easter egg... Or maybe more is hidden by it? Who knows o.o