Read their parsing statement in context:

> Markdown is that it's easy to read, and its second-biggest advantage is that it's easy to write. How easy it is to parse doesn't matter

After saying MD is "easy to read" the meaning of "parsing" is clearly limited to automated parsing by non-humans, and the only reasonable reading is "provided the markup is easy to read for humans, the difficulty in constructing an automated parser is irrelevant".

Reading is not sufficient. If you want it to produce the appropriate HTML, you must parse too.

When you write a file name a_b_c in one place, and a mathematical expression a*b*c in another place, and you don’t want to use `code formatting`, you need to know Markdown’s rules. Because otherwise, you’ll write a*b*c and get abc, instead of writing a\*b\*c to get a*b*c.

(And those are only the exact rules if you’re using CommonMark. On another engine, it might behave differently.)

If you only want to read, don’t use Markdown. But if you want to process as well, you need to know the processing.