The event might have been outdoors, but I bet there were organizational group meetings indoors. So they may have thought they were being careful, but they weren't. It happens. Most people don't have a clue how to keep from spreading a virus. They do five things right, and completely miss the sixth. They probably assumed their friends at those meetings "were clean", and the general public at the event was "suspect". That's a very common assumption.

I know from personal experience: I spent some time doing experimental surgery and working in operating rooms in my youth, so I have very good training in maintenance of sterile technique. My wife is a Veterinarian, and her sterile technique has always been a bit haphazard. I think the difference in our training is because lawsuits for nosocomial infections of people are much more expensive and have more serious career repercussions, than such infections of pets. That difference continues to this day, decades later. I am much more careful, quarantining packages and mail, etc. She goes shopping at Costco and buys stuff we can't quarantine or wash.

Educating anyone benefits everyone.