This code doesn't appear to prevent scrolling the page on iOS Safari. From some quick debugging, the most likely explanation is that it binds its touchMove handler during its touchStart handler, leading Safari to not call the touchMove handler until after a finger is released from the drag action. If it were to bind its touchMove handler before the touch begins, then the touchMove handler is called immediately, and scrolling can be prevented.
This code doesn't appear to prevent scrolling the page on iOS Safari. From some quick debugging, the most likely explanation is that it binds its touchMove handler during its touchStart handler, leading Safari to not call the touchMove handler until after a finger is released from the drag action. If it were to bind its touchMove handler before the touch begins, then the touchMove handler is called immediately, and scrolling can be prevented.