Hi.
You see the visual bounding boxes of the two paths.
It's a bit confusing, because the visual bounding box is based on rounded cap style, while you used butt cap.
If you change to square cap, there would be no "gaps" between the edge of the line and the visual bounding box.
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.html But you are probably not on the right track on drawing an "L" from two paths.
If you are after a simple "L" shape, one path, with three nodes and two segments in between would be only necerssary.
You can use the pen tool to draw that, with no need of rotating, aligning (and for joining the two paths and removing unnecessary nodes).
Just use the pen tool (Shift+F6),
click on the canvas, hold Ctrl and click somewhere below, then
hold the Ctrl key and click somewhere to the right, then press Enter.