I think most likely the notes were the result of re-processing information written down earlier -- if the original content was taken from a class. Nevertheless, that is very impressive -- almost a product of art. I wish I could get one copy.

Any such notes are most likely rewritten form of rougher notes written elsewhere. Then again, it's not difficult to write without making a mistake.

Think about musicians who improvise for quite a long time, playing hundreds of bars, while never playing a wrong note.

My notes looked like crap almost always, but I knew some girls in university where notes looked good while writing and then exactly did this rewriting for perfectionism (and besides that, this written reiteration is likely quite good to ingrain it, like spaced learning).

My parents can write like that (or could when they were not in their 90s yet). School back then put a lot of emphasis on good handwriting.

I on the other hand have handwriting that's barely legible after decades of typing on keyboards.