Where is this?
I’ve got a suspicion that, if it’s in the UK, your question is answered by the term “non-competitive race”…
Racing, when it uses public roads is very tightly regulated (be it for bikes or anything else), however anyone can come along and set up a non-competitive event, you only have to look at the massive rise in the number of Sportives to see that. There are no real regulations for that, you don’t need police permission or anything (although it’s common courtesy and good sense to advise them that there will be such an event), you can charge what you want etc but unfortunately there are a few organisers who basically run them as unauthorised races, hence the secrecy. 🙁
The insurance implications for if (when) something goes wrong don’t bear thinking about.
Got any details of the event? Even just the name/date/location?