Honestly...why do you think this? Whether concealed or open carry, the defensive capability is the same.
Open carry, screams...DONT ATTEMPT TO ROB ME....DONT ATTEMPT TO KILL ME OR MY FAMILY....DONT JACK WITH ME!
Well, the fact that the local citizens are "alarmed", articles are being written, this has become national news, and we're now debating it, should be your first clues.
I suppose if your guideline in life is, "Is this legal or isn't it?", then I can understand why you're perplexed. But there are other factors -- morality, common sense, civility, courtesy, manners, respect for others, consideration, etc. -- that come into play when operating within a society.
If everyone in that city, or most everyone, walked around carrying guns I'd feel differently. But it appears as though these are the only two. Plus they're teens and they're doing it, not because they've been threatened or because they feel unsafe, but because they can.
Of course they have a right to do it. Just as you have the right to say "F$%^" in public. Just don't be surprised when your "right" to do that is curtailed because you've abused it once too often.
"Open carry, screams...DONT ATTEMPT TO ROB ME....DONT ATTEMPT TO KILL ME OR MY FAMILY....DONT JACK WITH ME!"
In their case, open carry screams, "Look at me!"