I disagree. You can gauge your interns' level of knowledge *while* having a lesson plan, and an insight on why it merits teaching in the first place; just showing up for a hard-arranged tutorial completely unprepared and willing to just 'wing it' because you totally think you know your stuff and can't be bothered to prepare a structure, let alone a topic, just doesn't cut it.
If you *really* want to ensure you don't tread on previously covered ground, you prepare a couple of topics, and allow the students to choose. You don't just show up with coffee.
Also, seriously, there was no *actual* need for the smug retort at the end there really, was there? What are we, twelve?
In all seriousness, there's an epidemic of clinicians who haven't done a day's worth of formal teaching-skills education in their lives, who suck in teaching as a result, but think they're hot stuff because they know their medicine well. And when the clinician is unable to transmit his ideas, the students / interns get blamed instead. To bring it back to the original article, it's worse than "just read the code", it's more like "just read the code that's in my head".