It is a bit of a jump from what Ofsted actually say to what this journalist is alleging. Ofsted say they are exploring the use of data and information from social media and other sources to predict and prevent decline in school performance. That does not mean they will be "snooping on parents and pupils". It means they will be looking for mentions of the school on social media and tracking the school's reputation. They would only be looking at information posted publicly, i.e. information anyone can see.
This is fairly similar to the increasing number of companies that monitor their own reputation and that of their competitors on social media. The companies are not snooping on their customers, simply making use of information that people (customers and non-customers) choose to post publicly.
If you post something publicly on social media anyone can see it and make use of it. I really don't see that as snooping.
As a former Lay Inspector, we were provided with Census information which could be up to 10 years out of date, so I always checked local papers to see what they were reporting about the schools. It was around setting the school in context.