When I converted my curve to a mesh, I produced the correct mesh but the toolbox has unchecked “keep original” – exactly as in the video.
When I checked it, I created another object, a copy of the original non-mesh curve, (with 001 added to its name) – exactly as the lecture.
However I did not get the quick where the mesh gets ruined. Everything worked fine!
I’m using Blender 2.79b (on Ubuntu 18.04), so perhaps they have fixed this bug since Mikey’s lecture 