An error doesn't imply poor technique - the best in the world make errors. Observing and commenting on an error is not an indictment (in fact it is about 50% on an instructor's job). However, if there was no mechanical problem with the aircraft, and no freak wind condition, then there was at least one error made that caused such an extreme deviation in flight.
Could it have happened to me? Absolutely. Maybe I've been close to worse many times, and blissfully unaware (I know of one time when I definitely was).
Like I said earlier, making a mistake isn't desirable, but they happen every day. Let's be glad we have the ability to recover from them.
