That's one conclusion. The Stand could have brought in agency workers, it would have cost them more. Did they consider that option?
Legally they don't have a case as the precedent has been set in Graham v SEC and this is broadly similar. IE - That canceling an event because you dislike the beliefs of a speaker is unlawful.
The Stand may have had a strawman defence if they hadn't put out the statements they had. By arguing that they couldn't safely host the event and using health and safety as the grounds. However, they've already said its not the availability of staff per se but their availability to staff this particular event when they disagree with the speakers protected belief. That changes it significantly.
The whole thing is an unedifying spectacle. Those on the left cheering this as some sort of greater good and those on the right crying about free speech are as bad as one another imo.
As I alluded to earlier, JC is a self publicist and should be criticised for it. However, she has a right to her beliefs which are protected under the EA.