OP art was once called Kinetic art why did they
call it that?

The word kinetic means relating to motion. Since the early twentieth century artists have been incorporating movement into art. This has been partly to explore the possibilities of movement, partly to introduce the element of time, partly to reflect the importance of the machine and technology in the modern world and partly to explore the nature of vision.

Explanation:

( i looked it up so I'm not sure but i hope it does answer your question)