does anyone know how this figure was reached?
By presenting the consultation as only of concern to LGBT people. By not asking other stakeholder groups for their views. By writing it in a way that presupposes a belief in transgender ideology in respondents, therefore making it all but incomprehensible to anyone not steeped in it. By allowing responses to a proposed reform of a UK law to come from outside of the UK.
That responses were mass generated by email campaigns is neither here nor there - if it suited them, the recipients of such consultations have previously disregarded responses because they were of that nature and they have disregarded individual replies (see the survey on London's single-sex spaces for that tactic).
Looking at many other consultations on law reform, they aren't about quantity alone. They are about quality, too. Otherwise there'd only be a survey to fill in. They invite opposing views and arguments, because those writing law proposals can't think of every possible consequence when between them they may not have the necessary experiences.
Such as my friend who was responsible for the Equality Impact Assessment about changes to the out of hours GP service provided by our local health board. She organised many public and private meetings with stakeholder groups to solicit their views. By talking to them and answering their questions. Those of just one deaf blind local had a huge impact on her, because that was one patient group she had no experience in, and both the issues and proposed solutions were unknown to her.
The government did not organise such meetings, neither the UK one nor the Scottish one. However, the latter did organise such meetings on the proposed new Hate Crime Bill. I took part in one of them. The Law Commission organised public meetings seeking views on the proposal to reform the law on surrogacy.
To name but two law reform proposals treated very differently by the government.
That they did not do this for the GRA one, speaks volumes.