I thought it looked like lather, but it was curious too. As I understand it that was what all the barber hones actually directed for use as a lubricant.
That's how I understood it as well, but never hurts to try it dry. The hone I used for years, liked a progression of lubes, like my Washita. First oil, then water, then dry with light strokes. It was all I could push out of it.