After Svlasta saves the schoolkids from the stampede (becoming the "Hero of Eynsham Square" in doing so), the government recovers the dead body of the Faller that started the stampede. It is later revealed that the Faller had some sort of minuscule fibers inside its brain, something that had never been seen before. Later in the book, after transitioning to Nigel's POV, they deliberately eggsume a criminal they captured. One he is eggsumed, they invade his brain with a direct memory read, which sounds to be similar to the fibers mentioned above. Additionally, the description of the wound on the Faller's hand matches Kysandra shooting his hand and then having it repaired in their pod. Based on these two things, I'm assuming the Faller that caused the stampede is the same one that Nigel captured/interrogated/whatever.
How did that Faller end up at the square though? Did they send it deliberately? Can they control it? Did it escape? What happens to the Faller after they're done with the memory read is never explained, so I haven't figured out if this is Nigel attempting to deliberately cause Svlasta to become a hero (what were they going to do with the random innocent if nobody stopped the Faller?) or if it was coincidental and worked out somehow.