That video shows a few different things. The word “AxiDraw” is spelled out with a regular font, which consists of an outline that the machine follows, if you do watch the video closely. As it says in the manual, “All standard fonts are outline fonts […]. This means that when you do convert it to a path, it produces a hollow outline that your pen can follow.” This is normal and correct behavior.
The other text is written in single-stroke text (not regular fonts), specially designed for use with plotters. Again, as it says in the manual, you can use the Hershey Text utility to create single stroke text, and additional single-stroke fonts (of various types) are described in the URL given there, http://imajeenyus.com/computer/20150110_single_line_fonts/index.shtml