These are guidelines, rather than rules, and I suspect they reflect existing policies at individual schools. Unifying standards between institutions is a good thing.
Social media can be put to constructive use through formal pages, groups and so on (as reflected by the guidance) but befriending students online is really not very professional.
Child protection guidelines are fundamentally there to protect children, yes, but let's not forget that they are as much about protecting adults from allegations made by nefarious (or simply misunderstanding) kids by making it difficult for teachers to put themselves in compromising positions.
It's partly for this reason that schools and youth organisations have internal rules and regulations that say, for example, that driving a student home on your own is something you really shouldn't plan to do. Guidance covering responsible use of the Internet is just an extension to this
That said, I think that telling teachers to have "no expectation of privacy" really oversteps the mark.