On the Supreme Court website, the case summary says that there are two issues:
Did Stonewall Equality Ltd cause Garden Court Chambers to discriminate against Ms Bailey contrary to section 111(2) of the Equality Act 2010?
What is the correct approach to causation for the purposes of section 111(2) of the Equality Act 2010?
I think that perhaps one of the reasons why the court decided to hear the case is to consider what is "the correct approach to causation".
Causation, as far as I understand it, is asking the question "Did the defendant do something that caused the claimant a loss?"
That can apply in any situation, not just things connected with the Equality Act.
https://supremecourt.uk/cases/uksc-2026-0017