Sausagenbacon I have to say YABU. If you had explained a bit more, giving some good reasons for not doing the training, it might be different. As it is, you are rather blunt and leave us to assume you are right without giving us any information or evidence. 'Because it's stupid' is an opinion and tells us nothing. If the training were long and arduous, say every week for an evening meaning going out in the dark, making a difficult journey at your expense, and having to do homework, it might seem rather OTT for handing round cups of tea. But if it's just one session of listening to a talk and engaging in a discussion, then I can't see any reason for not attending. Surely anyone would want to enjoy the opportunity of learning about something new anyway.
I have been on the receiving end, whereby the C of E sent their most senior Safeguarding Officer to see me because of something I experienced. I was only too glad to meet her and her help made a huge difference. I know the Church of England has had its fingers burned by people working within it voluntarily and doing things that more than just offend others. I have many examples but they must remain in confidence. So the C of E are very keen to make sure this cannot happen, not anywhere.
You are not just handing out cups of tea. You are interacting with people. You are showing an alignment with the organisation, just by wielding the teapot, you have a position. The way you speak to people, look at them, your general demeanour, can have a big impression on the people to whom you serve tea in this context.
I think you should take up the chance to do the course. The opportunity to gain some self-awareness would not go amiss.