Yes you can draw sprites using multiple lines. For example you can draw a wireframe of a cube if you wish or create a character using lines. The goal is to draw the sprites using the line function, if you use sprite/texture drawing functions please indicate in your submission.
You may draw singular pixels using the line function, but using those singular pixels to reconstruct entire primitives is outside the spirit of the jam. So for example, using single pixels to create stars is okay, but using single pixels to create an entire filled ellipse is not so much. I would say this rule is subjective though, so it will not be strictly enforced.
Maybe next jam will be about using only a "pix" function!