Hi, I am following the course and can see, that you are filling faces to a quad with the shortcut F even though you have just three vertecies. Is that a setting or am I missing something here?
EDIT: I see Omar beat me to it, but here is my response as well!
Hey oockley, that's a good question! What you are seeing is actually an addon that comes with Blender, I use it so often I usually forget that it's not part of the base functionality (although it does ship with every download of Blender).
If you go to Edit>Preferences, and then go to the Addons header you should be able to look for the "F2" addon, this will allow you to close out faces and such by pressing "F" in various scenarios. There are several YT tutorials on how to use it, as well as some documentation here if you were looking for more information.
I hope that helps, thanks for leaving a question!
Chunck :)
Even with this addon enabled it doesn't create quad, when I press F, only connects those three vertices.
Make sure, that of those 3 Vertices, you only select the 'middle' one, the one in the concave corner. If you have all 3 Verts selected, F will fill it with a Triangle of course, as it should!