وَمَا رَمَيْتَ إِذْ رَمَيْتَ وَلَـٰكِنَّ ٱللَّهَ رَمَىٰ
“And it was not you [O Prophet] who threw [a handful of sand at the disbelievers], but it was Allah who did so”
This is the specific asbab al-nuzul: this ayah ("you did not throw when you threw, but it was Allah who threw") was revealed about this exact moment -- the Prophet ﷺ throwing a handful of pebbles that blinded the Quraysh line.