Cats DO arch their backs in anticipation of being petted. It's a great honour to you. Kittens will also arch, move sideways and scamper off in play.
I do the same thing to discourage counter surfing and all my cats and kittens still play/played with me.
I don't think it's anything at all to worry about though it would be nice to see this in action just in the wierd off chance it is. My first guess though, sounds like a normal playful scally rag of a kitten.