S/he wasn't standing a great deal nearer the race than many other spectators. I don't think anyone had any reason to pull him/back. Problem was they turned round and swung an effing big placard into the way. I don't think anyone could foresee that, especially not Tony Martin.
I can feel a bit of sympathy for him/her because this was a case of thoughtlessness, unlike those who run alongside the riders where it is nobeddery aforethought.
If people want to follow one rule then "never turn your back on the riders" would be a good one to start with. Followed by "keep your dog under control" and "don't be an utter nob". And maybe "if 8 year olds want trinkets from the caravan they had better be prepared to fight for them".
The message was "Allez Opi Omi" Twitter tells me that this means "Allez Granny and Gradad" in German. Kind of ironic that it was two German riders who came off the worst.