Wearing jerseys on 'lesser' events, my take on it is that I wouldn't buy a jersey I didn't expect to wear.
I get asked about cycling-specific kit (particularly lycra) by newbie cyclists from time to time. My answer is that cycling is my hobby, and I do long distance rides and multi-day tours where comfortable clothes made with lightweight, quick-drying technical materials are important. So when I go to the cupboard to select clothes for a sociable pootle, I'm likely to end up choosing Proper Cycling Kit™, because it's the best thing[1] there for the job (particularly if I'm riding at higher levels of effort to/from the ride). But that doesn't mean you need it to ride to the shops, and if that's all you're doing then anything weather-appropriate that's Not Jeans will suffice.
I reckon wearing an audax jersey to a Skyride (or a marathon T-shirt to a Parkrun) could simply be a case of that. You're advertising an event or organisation, but not necessarily willy-waving about it, and it might simply be a case of what was clean in the drawer.
[1] I avoid cycling in civvies in order to reduce wear on my civvies as much as comfort. Saddles destroy trousers, and buying trousers is hell.