As a government worker: we're constantly told to look for new and cheap ways of engaging with the public all the time, to find out what they think of policies and so on. The traditional alternatives are holding meetings and focus groups and running consultations - the former are expensive and often unrepresentative of the wider public, the latter can be expensive, risk not asking the right questions, and again don't always reach a representative section of the public.
I wouldn't be at all surprised if the Dept for Education has decided to try telling their comms team to go online and join in conversations, especially to do myth-busting. My dept have done similar, usually in mainstream newspapers and specialist magazines, but wouldn't be surprised if the weekly media coverage analysis now includes Mumsnet!
How Mumsnet confirm that DeptforEducation really does represent DfE is another question.