I did read that part, I still do not see how that justifies closing the museum terrace. The people photographing and sharing online pictures from the flat isn’t on the museum. Make the museum forbid to take pictures from the terrace if that’s the main source of concern. The museum didn’t create the terrace with the intent to showcase the inside of the flats as far as I can tell, it seems they had the permit to build it before the building existed.
Of course it's on the museum, this was an entirely predictable outcome.
And, as I understand it, it was the Tate's initial failure to do anything to restrain their visitors that caused the Supreme Court to decide as they did.
It's worth noting that it has since re-opened - but access to the side directly overlooking the flats is restricted, and there are now signs asking visitors not to take intrusive photos: https://www.timeout.com/london/news/the-tate-modern-has-reop...