Having had a quick look, it looks like they decided that Stonewall's actions were not intended to cause GCC to take action against AB - causation has a very precise legal definition.
Not being a lawyer, I can't comment on that.
But I did find the 'scene-setting' a bit off
14 Stonewall is a charity committed to advancing the rights of gay, lesbian, bisexual and trans people (“LGBT”). In 2015, it turned its attention to transgender issues and campaigned for gender recognition reform, setting up the Stonewall Trans Advisory Group (“STAG”) as an interface between Stonewall and other trans groups. Stonewall campaigned for inclusion for trans people, as well as for gays, lesbians and bisexuals. It devised a Diversity Champions Scheme to promote inclusion for the groups it represented in workplaces.
15 Stonewall’s support of trans rights, and in particular its support for self-identification under the Gender Recognition Act 2004, created tension with some of Stonewall’s traditional supporters, including lesbians such as Ms Bailey, who felt threatened by people with male bodies who identified as women. Some women with gender critical beliefs campaigned for same sex spaces and felt alienated by the accusation that it was transphobic.
This is unsubtle to say the least: Stonewall was not set up to advocate for trans people, as admitted by saying:
In 2015, it turned its attention to transgender issues
and the 'tension' felt by some traditional supporters was a matter of principle about Stonewall's role in representing same-sex-IDed people, not transgender people.
To say that the 'tension' was because, for instance,
'lesbians such as Ms Bailey, who felt threatened by people with male bodies who identified as women.'
is completely missing the point and reduces AB's and others' beliefs to fear of
' people with male bodies who identified as women'.
AB and others were motivated by principle, not by fear.
And the fact that they were 'alienated by the accusation that it was transphobic'
from the very organisation that had been established to defend their rights is a bigger deal than indicated by just one sentence.
I think this section of the judgement shows either an ignorance of the context of the case, or a bias in favour of an established LGB organisation changing its remit to include transgenderism.