I'm not sure the post really says anything about when such "true understanding" is necessary. That's a whole different can of worms.

Agreed, I may never "truly understand" how a programming language works, but there is a moment of clarity when you can say you really do understand why they did it that way. There are, of course, multiple levels to that. You may not know "how" they did it, but you do understand why aside from repeating what others have said on "why" they chose that approach.