I did this drawing quickly the other night when I was tired, and I promptly fell in love with it. I had been drawing for a project using a fine round tip brush and India ink. On a whim I decided to try doing a quick contour drawing the same way I draw using a ballpoint pen.
I have tried translating the same technique using a fountain pen, and it does not work. The key to the ballpoint drawings is the pen's flow. Because of the ball-tip the line is continuous and does not have hard stops. Conversely, the fountain tip makes drawings that are made up almost exclusively of hard stops because you are dragging tips of metal across the page. This means it is great for cross-hatching, but not so great for flowing contours.
Anyway, I tried the contour drawing with the brush and ink and immediately knew that this would work. It flows nearly as well as the ballpoint pen, except when you have to stop to dip the brush back in the ink. However, this is more than made up for by the dynamic line variation and even tonal variation as the brush loses ink.
I am sure that is more than you wanted to know.
Shifting gears, after staring at the drawing for a while, I think I discovered why it appeals to me so much: it looks like a drawing of Lupin or Daisuke Jigen from The Castle of Cagliostro.
If you have not seen this movie, you should. It is one of Miyazaki's early greats.