I think all or at least most Linux distributions include pen testing tools in their official repositories, Kali Linux just ships them out of the box. It seems that most kids using Kali Linux do it because it's "elite" or whatever, they don't know how to actually use it. I'm much more worried about a kid running Debian than one running Kali Linux, if only because Debian isn't "cool" so they must actually know what they're doing.

That being said, I don't expect law enforcement to be that sophisticated.

Unfortunately this HN article title has "Linux etc", and not specifying any specific distro.