I thought that wouldn't be funny for me since I'm a native English speaker but I've never heard these songs before (and the singers aren't singing very clearly...) that it does sound like Japanese! Though, I probably wouldn't have heard it that way if I weren't reading along with the lines. Haha, I love 空耳! The Metalica one was hilarious. Thanks for posting Siokan!
I've got an 「英語しか聞こえない」 video I'd like to share, I wonder if it's funny to you as a Japanese speaker. It's kinda lame but some parts are funny. "With 4 wheels, It's more safe! It's got friction!" part and the end sounds waaay too much like English.