Maybe they came from the other way and they haven't crossed it
When a UXB was discovered in the city where I live, the authorities evacuated and cordoned off the city centre - they did a crap job and I walked out of my workplace into the evacuated area (still unaware of the facts but 'in possession' of some rumours). I walked along the footpath towards the 'safe' area and got turned back by a 'community liaison officer' (pretend policeman) because he wasn't allowed to let anyone past the tape!!!

I walked past where the bomb was before a real copper asked me to cross the tape

I met a few other people in a similar predicament - 'caught' in the no-go zone looking for a way out!