I have seen how people ride at the London Freewheel, the Tour de Commute along with how they ride in the various parks around the smoke.
There is no way I would release 27000 in one go before a pro race. Even without accidents there will be bottlenecks, punctures, hills, random stopping, people who have never ridden in a group bigger than five, etc etc
I really doubt they had a chat to BHF about their wee ride, with more riders, deaths etc etc.
As for the beep, it sounds like they asked the people who runs TdF and other races for help. Just like they did at the 2012 race/time trail where Wiggo came across the line without a clue to how he had done. Asking as in - yeah I have seen a TdF highlight on C4 a few years back, I'm sure we can do this too, looks easy enough.