Shirts and pants have existed a long time, but clothing designers still design new ones. This isn't an exact copy of someone else's, it just uses the same principles, so yes, it is "designed".

You would say "I designed a t-shirt" not "I designed a clothing that has short sleeves".

It could just be a casual title, guy probably didn't even mean to title it that way but he probably didnt think about it too much. But to downvote because I point out something factually incorrect is just absurd.

Haha lol. Downvotes for saying "building" is not "designing". Why? Seriously people are so open-minded , very tolerant, just as long as you don't upset their feelings. Hahah

You're confusing design with invention. People design new instances of existing classes of object all the time, from shoes, to cars, to shirts. We call this profession "design", in fact. It's what the OP did with the cube: designed one.

I agree that "design" in the title is misleading. The main novelty of this cube is that it balances itself etc, and that was thought of and designed 12 years ago at ETH.

Nonetheless, incredible work by the OP - "I built a cube that balances itself" is already extremely impressive

He didn't invent it and doesn't claim he did but he did design each and every part that could not be bought off the shelf as well as the final assembly. I'd say 'design' is more than appropriate.