No way, this is such a common sentiment among my friends and coworkers that it needed to be said. This guy was straight up lazy and he got caught with his pants down.
Words don't need to be said; words don't have needs. People sometimes could benefit from hearing words. But if you're going to be a jerk about it, then people generally aren't going to listen. Ergo, no benefit.
In this case, though, I don't think stating the obvious was anything that the original poster needed to hear. You were responding to something where he already said that he was "a dummy" and will do it differently next time.
And I think your accusation of laziness is... unevidenced. He's a college sophomore at a selective school, he's studying half-way around the world from home, he has a number of neat projects on his blog, and decided to make a cross-country trip over Thanksgiving break. And in a follow-up to a theft, he took the time to post something to help other US visitors avoid thefts in the future. That doesn't look lazy to me.
There are two kinds of feedback. The one that makes people stronger, and the one that makes people weaker.
I believe it's so much more worthwhile to be supportive. When you have any kind of an adventage over others such as when you know something better, have move experience, have more money etc., you have these two options: either use your adventages to help, or to bring down.
To ridicule is not the best method of educating others either. And a person who feels strong doesn't have to show any sign of superiority, because with true strength comes security.
I wish the author of the original question will not find it too difficult to get back on track after loosing the bag. Good luck to you.