I didn't know handball was played by doing handstands.
But seriously, that's the first time i hear that argument. 99% of field sports are played on foot, that's a terrible criteria. Football is obviously called that because you use your feet (primarily) to manipulate the ball. In handball you manipulate the ball using your hands. In basketball, you put the ball in the basket. Name contains words that are directly related to the activity performed. Besides having no ball and not using feet (primarily) American football plays nothing like a football game. It's definitely a misnomer.
Curved relative to what?
Edit: Nvm, I understood what you mean. But I think it's a pedantic take. They obviously mean it in the context of the surface of the sphere.