I'm not saying that adding extraneous comments at the top of your file is the end of the world: I'm saying that Sal violated basic programming practice in one of the simplest 10 line programs that can be written. This is a canary.
What makes good teachers so good is that they know their field so well that they can use all of their gathered knowledge to help clarify and guide people who don't know any better. It doesn't matter how good a teacher you are if you really don't know what you're teaching.