Possible, but there's ample evidence around the Yxa (Swedish name for axe) theory. Even use in a similar context: https://i.stack.imgur.com/LNTu2.jpg https://i.stack.imgur.com/xzaQ9.jpg And it matches the "U" for "U-Boat", which apparently would be more common in Swedish (Ubåt) to refer to a submarine. It does require you believe whoever made the ball mixed Swedish and English, which seems possible given that it is a Chinese knockoff of a Hedstrom product.

"Ubåt" is the most common word for submarine in Swedish, and there is also a little used longer version "undervattensbåt" which also starts with "U".

The top response is far more convincing (it's a loan word from Swedish, and it's a knock-off ball, making such mistakes more likely).