Obviously it was a (hilarious) mistake.
They did not have the race course roped or fenced off.
That’s completely impractical. You can’t erect crowd barriers on a 2000+ mile route of public roads. Roadside crowds have been part of the TdF for the last 100+ years. There’s a rolling police motorbike escort which moves in front of the peloton to ensure spectators aren’t obstructing the road.
HOW many miles do you think this race covers???