The stages are designed by Erik Severson and Mike Millikan and sent to the league. Mike is our local match director and I've seen (but not read) a course of fire before it was submitted. It was nothing but written text.
So the diagrams are created at the national level. I suspect that they just use the same software to create the diagrams as they do for the COF PDFs. Looking at the properties of one of the PDF files I see that it was created in Adobe Photoshop CC 2019 (Macintosh).