Your employees would be temporarily representing me while they interact with customers who want to participate in a workshop. And I can't take the risk of employees alienating customers with rudeness and damaging my reputation.
I think you handled this brilliantly, and this bit here raises a very good point.
There's a certain chain of shops here that my friends and I only go into as a very last resort (which, thankfully isn't often). (Spotlight craft shops for anyone in Australia). I don't know what it is, but 90% of the time the employees are very stroppy - disinterested, rude, whatever.
Rightly or wrongly, I/we now tar all employees associated with that store with the same bad name as the rude people, and that applies to people doing demos etc in the store. They may be independent contractors completely unaffiliated with the actual store, but most people (myself included) neither know nor care about that; we just see a person working in the store and assume (A) they're Spotlight employees, and (B) they're likely to be just as rude as their colleagues. I know that's unfair, but sometimes a businesses' reputation can have long reach consequences for everyone involved.