I would say that the instructor's solution is geared towards readability, but that in some cases this coincides with code that is more efficient.
To quote Martin Fowler: "Any fool can write code that a computer can understand. Good programmers write code that humans can understand."
We encourage readability first, and when you have reached a solution that is clear and easy to understand, then (and only then) would you optimize for performance, and then only if necessary.
To quote Donald Knuth: "Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and these attempts at efficiency actually have a strong negative impact when debugging and maintenance are considered. We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%."
There are times when obvious optimizations would be silly to ignore. We tend to point those out