Yes. And the image you provided is a perfect example of a digital Line Drawing. The gap in the center is a style of Line Art. The thickness of the line denotes how deep verses how shallow the object is. The thicker the line the deeper that part is on the object.
This phenomenon happens because line drawings have little to no shadowing/shading. In a realistic rendering there would be some form of shadowing at the corners of the mouth and under the lip, but in a line drawing there is no shadowing - instead they make the line thicker to represent shadow...the gap in the middle is where the lips meet at the shallowest point - if you were shading the lips you would use hardly any shading at the center and it would look almost as if the top lip and bottom lip were becoming one - if the lips were to become one without shading...there would be no line separating them, thus...gap.
I hope I typed that in a way that made sense.