Doesn’t matter if he was unarmed or had his clothes on. Did this ‘teen’ present himself as an active threat to any officer or did he resist arrest? I bet yes to one or both.
You say people who resist arrest can be shot dead by police. But that’s unacceptable in a free country. If your son was having a psychotic breakdown, running naked in the street and defying police orders, you really believe shooting him dead would be an acceptable solution?