Here’s what I think happened. A few anti-GC people would create troll threads to try to discredit Mumsnet, then screenshot them immediately before they were deleted.
They would then send the screenshots to any of a handful of anti-GC Twitter accounts with large followings, who would obligingly tweet them.
The same anti-GC accounts would also tweet screenshots from other Mumsnet threads. These were invariably small snippets taken out of context. For example, there might be a sarcastic comment from a thread about feminism, a lone troll post from anywhere, or a rare anti-vaxx comment from an overwhelmingly pro-vaxx thread.
These snippets would sometimes be presented as “Mumsnet thinks” and the tweeter would usually write a “correction”, which either insulted the person quoted, or referred to them condescendingly as “Madam”, “pet” or “oh Sharon dear”.
Funnily enough, I never once saw a link to the thread the quote came from. Either the anti-GC tweeters never saw the threads, or they were acting in bad faith. I wouldn’t like to guess.