So the terms that Inkscape uses are for the most part the ones used in the (technical) SVG spec, except for the customizations. Both what you were intending and what you got would be called 'paths' - that is, a series of nodes connected in sequence. The difference would be that the path you want would be line-like, having a beginning and an end-node. The autotracer gives you a loop-like path, homeomorphic to a circle - this means the path makes the way along the sides of the line art. Because it is a closed path, it can enclose an area, which can then be coloured - a shape, in other words. The autotracer produces this because it cannot easily tell what is meant to be a shape in the raster graphic you give it, and what is supposed to be a line. Sure, one could probably write an extension that tries to recognize 'line-like' shapes and output paths accordingly, but the autotracer is too general-purpose to do that.
My suggestion would be to become familiar with the line (pen) tool, especially the Bezier mode (looking up 'spline' on Wikipedia [and related articles] might help understand what it is doing, especially if you are mathematically-minded), and to practice that - then if there are relatively few lines in your stick figure image, you can just draw over top and delete the raster when done. Obviously automating something is better than doing it by hand, but it does help you learn, and at some point you just have to get it done anyway.