Hi Ted - Blockchain is quite an advanced technology. The intent of this article was to explain the high level concept in simple language. There is a whole consensus mechanism in place to ensure who has the authority to make updates and how it is done. So, not everyone can become the "teacher" in the example. The core principle is just that instead of one central entity having the authority, it is now distributed (or decentralised). One needs to do quite a lot of research to understand it in detail :)

You can read more here about concensus mechanism here. Hope that help, cheers :)