Oh that's cool!! Looks like it's just a petal tip piped with a VERY steady hand and a good smooth turntable.
Or the tip you use for basketweave? Just turned around of course.
This look can also be accomplished by icing the entire cake smooth and using the tip of a round end spatula and a turntable to create the grooves.
Thanks... turning the turn table is going to be the challenge I think since I do not have a motorized one!
You need to practise. Because whether you do this with an icing bag or a spatula, you have to turn with one hand and pipe/ice with the other hand. It's as important to turn smoothly as it is to pipe smoothly.
But either way, you can stop and start overlapping the marks.