Its been a while since I researched Billy Joel but I agree with KaiMi, even though its clear the pen has issues in spots, I don't recall ever seeing so many small quick changes in direction. The flow seems off in ways I personally have never seen in any of his authentic signatures.
Billy was notorious for using an autopen ttm at times even with inscriptions but this isn't an autopen. Here is an example of his autopen. You can see the autopen shakes which are different than the changes in direction
And here is a JSA authenticated example I found quick which is more in line with what I remember with my research. His loops here are much smoother